New KMS properties come with a bunch of requirements to avoid each driver from running their own, inconsistent, set of properties, eventually leading to issues like property conflicts, inconsistencies between drivers and semantics, etc.
Let's document what we expect.
Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Alexandre Torgue alexandre.torgue@foss.st.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Alison Wang alison.wang@nxp.com Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Andrew Jeffery andrew@aj.id.au Cc: Andrzej Hajda a.hajda@samsung.com Cc: Anitha Chrisanthus anitha.chrisanthus@intel.com Cc: Benjamin Gaignard benjamin.gaignard@linaro.org Cc: Ben Skeggs bskeggs@redhat.com Cc: Boris Brezillon bbrezillon@kernel.org Cc: Brian Starkey brian.starkey@arm.com Cc: Chen Feng puck.chen@hisilicon.com Cc: Chen-Yu Tsai wens@csie.org Cc: Christian Gmeiner christian.gmeiner@gmail.com Cc: "Christian König" christian.koenig@amd.com Cc: Chun-Kuang Hu chunkuang.hu@kernel.org Cc: Edmund Dea edmund.j.dea@intel.com Cc: Eric Anholt eric@anholt.net Cc: Fabio Estevam festevam@gmail.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Haneen Mohammed hamohammed.sa@gmail.com Cc: Hans de Goede hdegoede@redhat.com Cc: "Heiko Stübner" heiko@sntech.de Cc: Huang Rui ray.huang@amd.com Cc: Hyun Kwon hyun.kwon@xilinx.com Cc: Inki Dae inki.dae@samsung.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Jernej Skrabec jernej.skrabec@siol.net Cc: Jerome Brunet jbrunet@baylibre.com Cc: Joel Stanley joel@jms.id.au Cc: John Stultz john.stultz@linaro.org Cc: Jonas Karlman jonas@kwiboo.se Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Joonyoung Shim jy0922.shim@samsung.com Cc: Jyri Sarha jyri.sarha@iki.fi Cc: Kevin Hilman khilman@baylibre.com Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com Cc: Kyungmin Park kyungmin.park@samsung.com Cc: Laurent Pinchart Laurent.pinchart@ideasonboard.com Cc: Linus Walleij linus.walleij@linaro.org Cc: Liviu Dudau liviu.dudau@arm.com Cc: Lucas Stach l.stach@pengutronix.de Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Marek Vasut marex@denx.de Cc: Martin Blumenstingl martin.blumenstingl@googlemail.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Maxime Coquelin mcoquelin.stm32@gmail.com Cc: Maxime Ripard mripard@kernel.org Cc: Melissa Wen melissa.srw@gmail.com Cc: Neil Armstrong narmstrong@baylibre.com Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: NXP Linux Team linux-imx@nxp.com Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: Patrik Jakobsson patrik.r.jakobsson@gmail.com Cc: Paul Cercueil paul@crapouillou.net Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pengutronix Kernel Team kernel@pengutronix.de Cc: Philippe Cornu philippe.cornu@foss.st.com Cc: Philipp Zabel p.zabel@pengutronix.de Cc: Qiang Yu yuq825@gmail.com Cc: Rob Clark robdclark@gmail.com Cc: Robert Foss robert.foss@linaro.org Cc: Rob Herring robh@kernel.org Cc: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Roland Scheidegger sroland@vmware.com Cc: Russell King linux@armlinux.org.uk Cc: Sam Ravnborg sam@ravnborg.org Cc: Sandy Huang hjc@rock-chips.com Cc: Sascha Hauer s.hauer@pengutronix.de Cc: Sean Paul sean@poorly.run Cc: Seung-Woo Kim sw0312.kim@samsung.com Cc: Shawn Guo shawnguo@kernel.org Cc: Simon Ser contact@emersion.fr Cc: Stefan Agner stefan@agner.ch Cc: Steven Price steven.price@arm.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thierry Reding thierry.reding@gmail.com Cc: Tian Tao tiantao6@hisilicon.com Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Tomi Valkeinen tomba@kernel.org Cc: VMware Graphics linux-graphics-maintainer@vmware.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: Xinwei Kong kong.kongxinwei@hisilicon.com Cc: Yannick Fertre yannick.fertre@foss.st.com Cc: Zack Rusin zackr@vmware.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Maxime Ripard maxime@cerno.tech
---
Changes from v3: - Roll back to the v2 - Add Simon and Pekka in Cc
Changes from v2: - Take into account the feedback from Laurent and Lidiu to no longer force generic properties, but prefix vendor-specific properties with the vendor name
Changes from v1: - Typos and wording reported by Daniel and Alex --- Documentation/gpu/drm-kms.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..c28b464dd397 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -463,6 +463,25 @@ KMS Properties This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections.
+Requirements +------------ + +KMS drivers might need to add extra properties to support new features. +Each new property introduced in a driver need to meet a few +requirements, in addition to the one mentioned above.: + +- It must be standardized, with some documentation to describe how the + property can be used. + +- It must provide a generic helper in the core code to register that + property on the object it attaches to. + +- Its content must be decoded by the core and provided in the object's + associated state structure. That includes anything drivers might want to + precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes. + +- An IGT test must be submitted where reasonable. + Property Types and Blob Property Support ----------------------------------------
On Wed, 16 Jun 2021 16:38:42 +0200 Maxime Ripard maxime@cerno.tech wrote:
New KMS properties come with a bunch of requirements to avoid each driver from running their own, inconsistent, set of properties, eventually leading to issues like property conflicts, inconsistencies between drivers and semantics, etc.
Let's document what we expect.
Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Alexandre Torgue alexandre.torgue@foss.st.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Alison Wang alison.wang@nxp.com Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Andrew Jeffery andrew@aj.id.au Cc: Andrzej Hajda a.hajda@samsung.com Cc: Anitha Chrisanthus anitha.chrisanthus@intel.com Cc: Benjamin Gaignard benjamin.gaignard@linaro.org Cc: Ben Skeggs bskeggs@redhat.com Cc: Boris Brezillon bbrezillon@kernel.org Cc: Brian Starkey brian.starkey@arm.com Cc: Chen Feng puck.chen@hisilicon.com Cc: Chen-Yu Tsai wens@csie.org Cc: Christian Gmeiner christian.gmeiner@gmail.com Cc: "Christian König" christian.koenig@amd.com Cc: Chun-Kuang Hu chunkuang.hu@kernel.org Cc: Edmund Dea edmund.j.dea@intel.com Cc: Eric Anholt eric@anholt.net Cc: Fabio Estevam festevam@gmail.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Haneen Mohammed hamohammed.sa@gmail.com Cc: Hans de Goede hdegoede@redhat.com Cc: "Heiko Stübner" heiko@sntech.de Cc: Huang Rui ray.huang@amd.com Cc: Hyun Kwon hyun.kwon@xilinx.com Cc: Inki Dae inki.dae@samsung.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Jernej Skrabec jernej.skrabec@siol.net Cc: Jerome Brunet jbrunet@baylibre.com Cc: Joel Stanley joel@jms.id.au Cc: John Stultz john.stultz@linaro.org Cc: Jonas Karlman jonas@kwiboo.se Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Joonyoung Shim jy0922.shim@samsung.com Cc: Jyri Sarha jyri.sarha@iki.fi Cc: Kevin Hilman khilman@baylibre.com Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com Cc: Kyungmin Park kyungmin.park@samsung.com Cc: Laurent Pinchart Laurent.pinchart@ideasonboard.com Cc: Linus Walleij linus.walleij@linaro.org Cc: Liviu Dudau liviu.dudau@arm.com Cc: Lucas Stach l.stach@pengutronix.de Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Marek Vasut marex@denx.de Cc: Martin Blumenstingl martin.blumenstingl@googlemail.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Maxime Coquelin mcoquelin.stm32@gmail.com Cc: Maxime Ripard mripard@kernel.org Cc: Melissa Wen melissa.srw@gmail.com Cc: Neil Armstrong narmstrong@baylibre.com Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: NXP Linux Team linux-imx@nxp.com Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: Patrik Jakobsson patrik.r.jakobsson@gmail.com Cc: Paul Cercueil paul@crapouillou.net Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pengutronix Kernel Team kernel@pengutronix.de Cc: Philippe Cornu philippe.cornu@foss.st.com Cc: Philipp Zabel p.zabel@pengutronix.de Cc: Qiang Yu yuq825@gmail.com Cc: Rob Clark robdclark@gmail.com Cc: Robert Foss robert.foss@linaro.org Cc: Rob Herring robh@kernel.org Cc: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Roland Scheidegger sroland@vmware.com Cc: Russell King linux@armlinux.org.uk Cc: Sam Ravnborg sam@ravnborg.org Cc: Sandy Huang hjc@rock-chips.com Cc: Sascha Hauer s.hauer@pengutronix.de Cc: Sean Paul sean@poorly.run Cc: Seung-Woo Kim sw0312.kim@samsung.com Cc: Shawn Guo shawnguo@kernel.org Cc: Simon Ser contact@emersion.fr Cc: Stefan Agner stefan@agner.ch Cc: Steven Price steven.price@arm.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thierry Reding thierry.reding@gmail.com Cc: Tian Tao tiantao6@hisilicon.com Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Tomi Valkeinen tomba@kernel.org Cc: VMware Graphics linux-graphics-maintainer@vmware.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: Xinwei Kong kong.kongxinwei@hisilicon.com Cc: Yannick Fertre yannick.fertre@foss.st.com Cc: Zack Rusin zackr@vmware.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Maxime Ripard maxime@cerno.tech
Changes from v3:
- Roll back to the v2
- Add Simon and Pekka in Cc
Changes from v2:
- Take into account the feedback from Laurent and Lidiu to no longer force generic properties, but prefix vendor-specific properties with the vendor name
Changes from v1:
- Typos and wording reported by Daniel and Alex
Documentation/gpu/drm-kms.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..c28b464dd397 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -463,6 +463,25 @@ KMS Properties This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections.
+Requirements +------------
+KMS drivers might need to add extra properties to support new features. +Each new property introduced in a driver need to meet a few +requirements, in addition to the one mentioned above.:
+- It must be standardized, with some documentation to describe how the
- property can be used.
Hi,
I might replace "some" with "full" documentation. Also not only how it can be used but also what it does.
FYI, some common things that tend to be forgotten IME: - Spell out exactly the name string for the property in the documentation so that it is unambiguous what string userspace should look for. - The same for string names of enum values. - Explicitly document what each enum value means, do not trust that the value name describes it well enough. - Explain how the property interacts with other, existing properties.
Not sure if these should be written down here or anywhere though. Interaction with other properties is kind of important.
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Would it be too much to replace "where reasonable" with "if it is at all possible to write a test."?
How about adding the following somewhere?
- The initial state of the property (set during driver initialization) must match how the driver+hardware behaved before introducing this property. It may be some fixed value or it may be inherited from e.g. the firmware that booted the system. How the initial state is determined must also be documented, that is, where does it come from.
The initial state must not be called "default", because I want to reserve the term default for something else if possible: the phrase "reset everything to defaults", which is a whole another discussion.
How about also saying that fbcon/fbdev must set this property when taking over? That sounds to be like a common omission leading to funky KMS state in fbcon. The value fbdev sets it to only needs to make sense to fbdev, and it does not need to be ~~the initial value~~ nor the default value. Or are we hoping to kill fbcon in favor of a userspace kmscon soon? ;-)
Ooh, maybe the KMS property documentation should also say what value fbdev will set the property to. That's kind of UABI, because userspace probably implicitly relies on it in many cases. ...which means fbdev should set the property to its initial value, otherwise userspace will break.
Thanks, pq
Hi Pekka,
On Thu, Jun 17, 2021 at 11:20:36AM +0300, Pekka Paalanen wrote:
On Wed, 16 Jun 2021 16:38:42 +0200 Maxime Ripard maxime@cerno.tech wrote:
New KMS properties come with a bunch of requirements to avoid each driver from running their own, inconsistent, set of properties, eventually leading to issues like property conflicts, inconsistencies between drivers and semantics, etc.
Let's document what we expect.
Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Alexandre Torgue alexandre.torgue@foss.st.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Alison Wang alison.wang@nxp.com Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Andrew Jeffery andrew@aj.id.au Cc: Andrzej Hajda a.hajda@samsung.com Cc: Anitha Chrisanthus anitha.chrisanthus@intel.com Cc: Benjamin Gaignard benjamin.gaignard@linaro.org Cc: Ben Skeggs bskeggs@redhat.com Cc: Boris Brezillon bbrezillon@kernel.org Cc: Brian Starkey brian.starkey@arm.com Cc: Chen Feng puck.chen@hisilicon.com Cc: Chen-Yu Tsai wens@csie.org Cc: Christian Gmeiner christian.gmeiner@gmail.com Cc: "Christian König" christian.koenig@amd.com Cc: Chun-Kuang Hu chunkuang.hu@kernel.org Cc: Edmund Dea edmund.j.dea@intel.com Cc: Eric Anholt eric@anholt.net Cc: Fabio Estevam festevam@gmail.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Haneen Mohammed hamohammed.sa@gmail.com Cc: Hans de Goede hdegoede@redhat.com Cc: "Heiko Stübner" heiko@sntech.de Cc: Huang Rui ray.huang@amd.com Cc: Hyun Kwon hyun.kwon@xilinx.com Cc: Inki Dae inki.dae@samsung.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Jernej Skrabec jernej.skrabec@siol.net Cc: Jerome Brunet jbrunet@baylibre.com Cc: Joel Stanley joel@jms.id.au Cc: John Stultz john.stultz@linaro.org Cc: Jonas Karlman jonas@kwiboo.se Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Joonyoung Shim jy0922.shim@samsung.com Cc: Jyri Sarha jyri.sarha@iki.fi Cc: Kevin Hilman khilman@baylibre.com Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com Cc: Kyungmin Park kyungmin.park@samsung.com Cc: Laurent Pinchart Laurent.pinchart@ideasonboard.com Cc: Linus Walleij linus.walleij@linaro.org Cc: Liviu Dudau liviu.dudau@arm.com Cc: Lucas Stach l.stach@pengutronix.de Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Marek Vasut marex@denx.de Cc: Martin Blumenstingl martin.blumenstingl@googlemail.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Maxime Coquelin mcoquelin.stm32@gmail.com Cc: Maxime Ripard mripard@kernel.org Cc: Melissa Wen melissa.srw@gmail.com Cc: Neil Armstrong narmstrong@baylibre.com Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: NXP Linux Team linux-imx@nxp.com Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: Patrik Jakobsson patrik.r.jakobsson@gmail.com Cc: Paul Cercueil paul@crapouillou.net Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pengutronix Kernel Team kernel@pengutronix.de Cc: Philippe Cornu philippe.cornu@foss.st.com Cc: Philipp Zabel p.zabel@pengutronix.de Cc: Qiang Yu yuq825@gmail.com Cc: Rob Clark robdclark@gmail.com Cc: Robert Foss robert.foss@linaro.org Cc: Rob Herring robh@kernel.org Cc: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Roland Scheidegger sroland@vmware.com Cc: Russell King linux@armlinux.org.uk Cc: Sam Ravnborg sam@ravnborg.org Cc: Sandy Huang hjc@rock-chips.com Cc: Sascha Hauer s.hauer@pengutronix.de Cc: Sean Paul sean@poorly.run Cc: Seung-Woo Kim sw0312.kim@samsung.com Cc: Shawn Guo shawnguo@kernel.org Cc: Simon Ser contact@emersion.fr Cc: Stefan Agner stefan@agner.ch Cc: Steven Price steven.price@arm.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thierry Reding thierry.reding@gmail.com Cc: Tian Tao tiantao6@hisilicon.com Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Tomi Valkeinen tomba@kernel.org Cc: VMware Graphics linux-graphics-maintainer@vmware.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: Xinwei Kong kong.kongxinwei@hisilicon.com Cc: Yannick Fertre yannick.fertre@foss.st.com Cc: Zack Rusin zackr@vmware.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Maxime Ripard maxime@cerno.tech
Changes from v3:
- Roll back to the v2
- Add Simon and Pekka in Cc
Changes from v2:
- Take into account the feedback from Laurent and Lidiu to no longer force generic properties, but prefix vendor-specific properties with the vendor name
Changes from v1:
- Typos and wording reported by Daniel and Alex
Documentation/gpu/drm-kms.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..c28b464dd397 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -463,6 +463,25 @@ KMS Properties This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections.
+Requirements +------------
+KMS drivers might need to add extra properties to support new features. +Each new property introduced in a driver need to meet a few +requirements, in addition to the one mentioned above.:
+- It must be standardized, with some documentation to describe how the
- property can be used.
Hi,
I might replace "some" with "full" documentation. Also not only how it can be used but also what it does.
FYI, some common things that tend to be forgotten IME:
- Spell out exactly the name string for the property in the documentation so that it is unambiguous what string userspace should look for.
- The same for string names of enum values.
- Explicitly document what each enum value means, do not trust that the value name describes it well enough.
- Explain how the property interacts with other, existing properties.
Not sure if these should be written down here or anywhere though. Interaction with other properties is kind of important.
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Would it be too much to replace "where reasonable" with "if it is at all possible to write a test."?
How about adding the following somewhere?
- The initial state of the property (set during driver initialization) must match how the driver+hardware behaved before introducing this property. It may be some fixed value or it may be inherited from e.g. the firmware that booted the system. How the initial state is determined must also be documented, that is, where does it come from.
The initial state must not be called "default", because I want to reserve the term default for something else if possible: the phrase "reset everything to defaults", which is a whole another discussion.
I've taken into account your previous comments, thanks
How about also saying that fbcon/fbdev must set this property when taking over? That sounds to be like a common omission leading to funky KMS state in fbcon. The value fbdev sets it to only needs to make sense to fbdev, and it does not need to be ~~the initial value~~ nor the default value. Or are we hoping to kill fbcon in favor of a userspace kmscon soon? ;-)
Ooh, maybe the KMS property documentation should also say what value fbdev will set the property to. That's kind of UABI, because userspace probably implicitly relies on it in many cases. ...which means fbdev should set the property to its initial value, otherwise userspace will break.
I'm not sure about this one: fbdev and fbcon are still optional features of the kernel and can be disabled at the user discretion. Having any part of the user-space rely on the fbdev behavior seems a bit broken, especially when we have a mechanism to retrieve the state when the application starts.
Maxime
On Tue, 6 Jul 2021 10:52:02 +0200 Maxime Ripard maxime@cerno.tech wrote:
Hi Pekka,
On Thu, Jun 17, 2021 at 11:20:36AM +0300, Pekka Paalanen wrote:
On Wed, 16 Jun 2021 16:38:42 +0200 Maxime Ripard maxime@cerno.tech wrote:
New KMS properties come with a bunch of requirements to avoid each driver from running their own, inconsistent, set of properties, eventually leading to issues like property conflicts, inconsistencies between drivers and semantics, etc.
Let's document what we expect.
Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Alexandre Torgue alexandre.torgue@foss.st.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Alison Wang alison.wang@nxp.com Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Andrew Jeffery andrew@aj.id.au Cc: Andrzej Hajda a.hajda@samsung.com Cc: Anitha Chrisanthus anitha.chrisanthus@intel.com Cc: Benjamin Gaignard benjamin.gaignard@linaro.org Cc: Ben Skeggs bskeggs@redhat.com Cc: Boris Brezillon bbrezillon@kernel.org Cc: Brian Starkey brian.starkey@arm.com Cc: Chen Feng puck.chen@hisilicon.com Cc: Chen-Yu Tsai wens@csie.org Cc: Christian Gmeiner christian.gmeiner@gmail.com Cc: "Christian König" christian.koenig@amd.com Cc: Chun-Kuang Hu chunkuang.hu@kernel.org Cc: Edmund Dea edmund.j.dea@intel.com Cc: Eric Anholt eric@anholt.net Cc: Fabio Estevam festevam@gmail.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Haneen Mohammed hamohammed.sa@gmail.com Cc: Hans de Goede hdegoede@redhat.com Cc: "Heiko Stübner" heiko@sntech.de Cc: Huang Rui ray.huang@amd.com Cc: Hyun Kwon hyun.kwon@xilinx.com Cc: Inki Dae inki.dae@samsung.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Jernej Skrabec jernej.skrabec@siol.net Cc: Jerome Brunet jbrunet@baylibre.com Cc: Joel Stanley joel@jms.id.au Cc: John Stultz john.stultz@linaro.org Cc: Jonas Karlman jonas@kwiboo.se Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Joonyoung Shim jy0922.shim@samsung.com Cc: Jyri Sarha jyri.sarha@iki.fi Cc: Kevin Hilman khilman@baylibre.com Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com Cc: Kyungmin Park kyungmin.park@samsung.com Cc: Laurent Pinchart Laurent.pinchart@ideasonboard.com Cc: Linus Walleij linus.walleij@linaro.org Cc: Liviu Dudau liviu.dudau@arm.com Cc: Lucas Stach l.stach@pengutronix.de Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Marek Vasut marex@denx.de Cc: Martin Blumenstingl martin.blumenstingl@googlemail.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Maxime Coquelin mcoquelin.stm32@gmail.com Cc: Maxime Ripard mripard@kernel.org Cc: Melissa Wen melissa.srw@gmail.com Cc: Neil Armstrong narmstrong@baylibre.com Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: NXP Linux Team linux-imx@nxp.com Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: Patrik Jakobsson patrik.r.jakobsson@gmail.com Cc: Paul Cercueil paul@crapouillou.net Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pengutronix Kernel Team kernel@pengutronix.de Cc: Philippe Cornu philippe.cornu@foss.st.com Cc: Philipp Zabel p.zabel@pengutronix.de Cc: Qiang Yu yuq825@gmail.com Cc: Rob Clark robdclark@gmail.com Cc: Robert Foss robert.foss@linaro.org Cc: Rob Herring robh@kernel.org Cc: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Roland Scheidegger sroland@vmware.com Cc: Russell King linux@armlinux.org.uk Cc: Sam Ravnborg sam@ravnborg.org Cc: Sandy Huang hjc@rock-chips.com Cc: Sascha Hauer s.hauer@pengutronix.de Cc: Sean Paul sean@poorly.run Cc: Seung-Woo Kim sw0312.kim@samsung.com Cc: Shawn Guo shawnguo@kernel.org Cc: Simon Ser contact@emersion.fr Cc: Stefan Agner stefan@agner.ch Cc: Steven Price steven.price@arm.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thierry Reding thierry.reding@gmail.com Cc: Tian Tao tiantao6@hisilicon.com Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Tomi Valkeinen tomba@kernel.org Cc: VMware Graphics linux-graphics-maintainer@vmware.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: Xinwei Kong kong.kongxinwei@hisilicon.com Cc: Yannick Fertre yannick.fertre@foss.st.com Cc: Zack Rusin zackr@vmware.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Maxime Ripard maxime@cerno.tech
Changes from v3:
- Roll back to the v2
- Add Simon and Pekka in Cc
Changes from v2:
- Take into account the feedback from Laurent and Lidiu to no longer force generic properties, but prefix vendor-specific properties with the vendor name
Changes from v1:
- Typos and wording reported by Daniel and Alex
Documentation/gpu/drm-kms.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..c28b464dd397 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -463,6 +463,25 @@ KMS Properties This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections.
+Requirements +------------
+KMS drivers might need to add extra properties to support new features. +Each new property introduced in a driver need to meet a few +requirements, in addition to the one mentioned above.:
+- It must be standardized, with some documentation to describe how the
- property can be used.
Hi,
I might replace "some" with "full" documentation. Also not only how it can be used but also what it does.
FYI, some common things that tend to be forgotten IME:
- Spell out exactly the name string for the property in the documentation so that it is unambiguous what string userspace should look for.
- The same for string names of enum values.
- Explicitly document what each enum value means, do not trust that the value name describes it well enough.
- Explain how the property interacts with other, existing properties.
Not sure if these should be written down here or anywhere though. Interaction with other properties is kind of important.
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Would it be too much to replace "where reasonable" with "if it is at all possible to write a test."?
How about adding the following somewhere?
- The initial state of the property (set during driver initialization) must match how the driver+hardware behaved before introducing this property. It may be some fixed value or it may be inherited from e.g. the firmware that booted the system. How the initial state is determined must also be documented, that is, where does it come from.
The initial state must not be called "default", because I want to reserve the term default for something else if possible: the phrase "reset everything to defaults", which is a whole another discussion.
I've taken into account your previous comments, thanks
How about also saying that fbcon/fbdev must set this property when taking over? That sounds to be like a common omission leading to funky KMS state in fbcon. The value fbdev sets it to only needs to make sense to fbdev, and it does not need to be ~~the initial value~~ nor the default value. Or are we hoping to kill fbcon in favor of a userspace kmscon soon? ;-)
Ooh, maybe the KMS property documentation should also say what value fbdev will set the property to. That's kind of UABI, because userspace probably implicitly relies on it in many cases. ...which means fbdev should set the property to its initial value, otherwise userspace will break.
I'm not sure about this one: fbdev and fbcon are still optional features of the kernel and can be disabled at the user discretion. Having any part of the user-space rely on the fbdev behavior seems a bit broken, especially when we have a mechanism to retrieve the state when the application starts.
Hi,
yes, exactly that is why fbdev/fbcon should reset the properties to their initial values. You would not want userspace inheriting a different KMS state with vs. without fbcon when it starts.
Retrieving the current KMS state is useless if the current KMS state is somehow wonky and the application does not understand that specific KMS property that is wonky. It cannot set the property to any value other than it already had without user intervention.
I'd say fbcon causing all KMS state to be reset is a quality of life thing. It's possible to live without by rebooting, but it would certainly make at least developers' and testers' life easier until we get the real "reset KMS" knob (which fbcon could then use too).
Besides, even if it is broken for userspace to rely on the KMS state set by fbcon/fbdev, userspace is already doing that and not on purpose because new KMS properties get added in the kernel. I would bet that there is not a single userspace program that would actually set all KMS properties that drivers might expose. So they are depending on inherited KMS state, which could be left by driver initialization, by fbdev/fbcon, or by any other userspace.
But yeah, this idea is something new, so don't let this discussion delay landing the docs.
Thanks, pq
On Tue, Jul 06, 2021 at 12:37:23PM +0300, Pekka Paalanen wrote:
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Would it be too much to replace "where reasonable" with "if it is at all possible to write a test."?
How about adding the following somewhere?
- The initial state of the property (set during driver initialization) must match how the driver+hardware behaved before introducing this property. It may be some fixed value or it may be inherited from e.g. the firmware that booted the system. How the initial state is determined must also be documented, that is, where does it come from.
The initial state must not be called "default", because I want to reserve the term default for something else if possible: the phrase "reset everything to defaults", which is a whole another discussion.
I've taken into account your previous comments, thanks
How about also saying that fbcon/fbdev must set this property when taking over? That sounds to be like a common omission leading to funky KMS state in fbcon. The value fbdev sets it to only needs to make sense to fbdev, and it does not need to be ~~the initial value~~ nor the default value. Or are we hoping to kill fbcon in favor of a userspace kmscon soon? ;-)
Ooh, maybe the KMS property documentation should also say what value fbdev will set the property to. That's kind of UABI, because userspace probably implicitly relies on it in many cases. ...which means fbdev should set the property to its initial value, otherwise userspace will break.
I'm not sure about this one: fbdev and fbcon are still optional features of the kernel and can be disabled at the user discretion. Having any part of the user-space rely on the fbdev behavior seems a bit broken, especially when we have a mechanism to retrieve the state when the application starts.
yes, exactly that is why fbdev/fbcon should reset the properties to their initial values. You would not want userspace inheriting a different KMS state with vs. without fbcon when it starts.
I'm not sure I'm following you when fbdev/fbcon should reset these properties. When a master takes over?
If we consider fbdev as any KMS client, isn't it a fundamental change with how it's currently done? I haven't seen anywhere that a compositor (or any client for that matter) should put the KMS device in the same state that it started it with. In case of a crash it would be fairly difficult to achieve.
Retrieving the current KMS state is useless if the current KMS state is somehow wonky and the application does not understand that specific KMS property that is wonky. It cannot set the property to any value other than it already had without user intervention.
Yeah, that's true. But the same could be said if you switch from one client to the other for example, at the moment there's no guarantee that the first one didn't change a property to a value you don't expect in the second. Unless we manage to tie that somehow to a first open of the device?
I'd say fbcon causing all KMS state to be reset is a quality of life thing. It's possible to live without by rebooting, but it would certainly make at least developers' and testers' life easier until we get the real "reset KMS" knob (which fbcon could then use too).
Besides, even if it is broken for userspace to rely on the KMS state set by fbcon/fbdev, userspace is already doing that and not on purpose because new KMS properties get added in the kernel. I would bet that there is not a single userspace program that would actually set all KMS properties that drivers might expose. So they are depending on inherited KMS state, which could be left by driver initialization, by fbdev/fbcon, or by any other userspace.
But yeah, this idea is something new, so don't let this discussion delay landing the docs.
Ack, I've sent a new version
Thanks! Maxime
On Tue, 6 Jul 2021 18:42:41 +0200 Maxime Ripard maxime@cerno.tech wrote:
On Tue, Jul 06, 2021 at 12:37:23PM +0300, Pekka Paalanen wrote:
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Would it be too much to replace "where reasonable" with "if it is at all possible to write a test."?
How about adding the following somewhere?
- The initial state of the property (set during driver initialization) must match how the driver+hardware behaved before introducing this property. It may be some fixed value or it may be inherited from e.g. the firmware that booted the system. How the initial state is determined must also be documented, that is, where does it come from.
The initial state must not be called "default", because I want to reserve the term default for something else if possible: the phrase "reset everything to defaults", which is a whole another discussion.
I've taken into account your previous comments, thanks
How about also saying that fbcon/fbdev must set this property when taking over? That sounds to be like a common omission leading to funky KMS state in fbcon. The value fbdev sets it to only needs to make sense to fbdev, and it does not need to be ~~the initial value~~ nor the default value. Or are we hoping to kill fbcon in favor of a userspace kmscon soon? ;-)
Ooh, maybe the KMS property documentation should also say what value fbdev will set the property to. That's kind of UABI, because userspace probably implicitly relies on it in many cases. ...which means fbdev should set the property to its initial value, otherwise userspace will break.
I'm not sure about this one: fbdev and fbcon are still optional features of the kernel and can be disabled at the user discretion. Having any part of the user-space rely on the fbdev behavior seems a bit broken, especially when we have a mechanism to retrieve the state when the application starts.
yes, exactly that is why fbdev/fbcon should reset the properties to their initial values. You would not want userspace inheriting a different KMS state with vs. without fbcon when it starts.
I'm not sure I'm following you when fbdev/fbcon should reset these properties. When a master takes over?
Hi,
when fbcon/fbdev takes over. If it doesn't reset things like GAMMA LUT, it's possible it won't be readable even though nothing fails.
(Let's say you fumble with an xrandr incantation and manage to set a LUT that turns everything into a single shade of green or something. How do you recover?)
When a userspace KMS client hands off to another userspace KMS client, fbcon/fbdev should not do anything. If it did, that would cause extra flicker.
I'm assuming fbcon/fbdev already implement all the necessary mechanisms, but they just don't poke at all the KMS properties necessary, as is evident from e.g. Michel Dänzer's testing seeing wrong colors in fbcon after a userspace KMS client changed GAMMA or DEGAMMA once.
Handling this properly would offer an escape hatch without reboot when something goes wrong in a display server. It's not a fix for userspace KMS client handing off to another userspace KMS client, for that we need something else.
If we consider fbdev as any KMS client, isn't it a fundamental change with how it's currently done? I haven't seen anywhere that a compositor (or any client for that matter) should put the KMS device in the same state that it started it with. In case of a crash it would be fairly difficult to achieve.
It has long been agreed IMO but never implemented anywhere AFAIK that a userspace KMS client should fully reset the whole KMS state to the KMS state it started with when it *comes back* after being switched away. I have talked with Daniel Vetter about this several times over the years. The problem with resetting the full KMS state is what to do with those KMS properties the KMS client does not understand but are exposed by the driver.
When a userspace KMS client switches out or quits, what is implemented and what should be implemented differs again. I believe that KMS clients of today do not change anything, so that the number of modesets is minimized. This is sufficient if the KMS client didn't use any less commonly used KMS properties. It's also consistent with crash behaviour.
If the KMS client wants to support seamless hand-off to another KMS client, the practical approach is "reset everything to the sane KMS state except keep the video mode" so that if the next KMS client doesn't understand everything, it still works. I don't know if display servers care to implement this, or do they just assume switching to another instance of themselves in which case they know what the next KMS client does. Or maybe the don't even use KMS properties others don't use too.
Btw. Xorg understands very few KMS properties by itself I think. It just exposes everything via RandR and assumes that whatever X11 clients are running, some of them will take care of the KMS properties. So one cannot look at Xorg as a single entity, one also needs to look at all the different desktop environments and whatever.
Another idea that has come up is that userspace should invent a KMS hand-off protocol completely in userspace. I'm not aware of anyone working on that. It would allow better smooth KMS hand-off between KMS clients, as the current and the next KMS client could negotiate about which KMS properties they understand and which need to be reset abruptly.
In any case, consensus seems to be that when a KMS client switches back in, there are no guarantees at all about the KMS state it inherits at that point. Therefore fbcon as a KMS client needs to reset everything. People just don't seem to care about fbcon working that much.
There is also the assumption that when a KMS client starts, the KMS state it inherits is... "reasonable". This should be true if the KMS state is the initial state chosen by a driver, and also if the state has been touched by fbcon, because it's not uncommon for fbcon to be up before the first KMS userspace client starts. But after the first KMS userspace client has started, all bets are practically off for the next KMS client starting.
Retrieving the current KMS state is useless if the current KMS state is somehow wonky and the application does not understand that specific KMS property that is wonky. It cannot set the property to any value other than it already had without user intervention.
Yeah, that's true. But the same could be said if you switch from one client to the other for example, at the moment there's no guarantee that the first one didn't change a property to a value you don't expect in the second. Unless we manage to tie that somehow to a first open of the device?
As I wrote above, yes, this is an open problem. Fbcon being just a KMS client needs a solution like all KMS clients. None of it is a regression per se, unless you see adding new KMS properties that provoke this problem more as a regression.
The idea I've been pondering about is a flag in atomic commit: instead of basing the changes on the current KMS state, start with "the default KMS state".
The definition of the default KMS state is tricky, because it should not depend on e.g. firmware. So it is not the same as the initial KMS state programmed in driver initialization. It needs to be defined separately and individually for each KMS property. In my opinion, the default KMS state should be defined as everything being off (planes, crtcs), disabled (dithering, HDR), pass-through/identity (GAMMA, DEGAMMA, CTM), "auto" where that applies and is the initial state, and so on. The goal is to make it as neutral and as "off" as possible while still giving good chances of letting the simpler KMS clients work correctly.
If there was a mechanism for this "reset to default", fbdev could just hit it.
There have been opinions that this problem does not need solving, because an average Linux user will never switch between arbitrary KMS clients. At most, they switch from bootsplash to a login manager, and then to a desktop compositor. Bootsplash won't change "advanced" KMS state, and the login manager's display server acts as the resetting entity as it is maintained to explicitly(?) support all the different desktops. If a desktop uses a new KMS property, the login manager is updated(?) to reset that property.
Hence I didn't go all the way suggesting in the rules that the default state needs to be defined.
And if fbcon is good to leave rotting, then no need to mention that either.
I'd say fbcon causing all KMS state to be reset is a quality of life thing. It's possible to live without by rebooting, but it would certainly make at least developers' and testers' life easier until we get the real "reset KMS" knob (which fbcon could then use too).
Besides, even if it is broken for userspace to rely on the KMS state set by fbcon/fbdev, userspace is already doing that and not on purpose because new KMS properties get added in the kernel. I would bet that there is not a single userspace program that would actually set all KMS properties that drivers might expose. So they are depending on inherited KMS state, which could be left by driver initialization, by fbdev/fbcon, or by any other userspace.
But yeah, this idea is something new, so don't let this discussion delay landing the docs.
Ack, I've sent a new version
Thank you! pq
On 6/16/21 4:38 PM, Maxime Ripard wrote:
New KMS properties come with a bunch of requirements to avoid each driver from running their own, inconsistent, set of properties, eventually leading to issues like property conflicts, inconsistencies between drivers and semantics, etc.
Let's document what we expect.
Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Alexandre Torgue alexandre.torgue@foss.st.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Alison Wang alison.wang@nxp.com Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Andrew Jeffery andrew@aj.id.au Cc: Andrzej Hajda a.hajda@samsung.com Cc: Anitha Chrisanthus anitha.chrisanthus@intel.com Cc: Benjamin Gaignard benjamin.gaignard@linaro.org Cc: Ben Skeggs bskeggs@redhat.com Cc: Boris Brezillon bbrezillon@kernel.org Cc: Brian Starkey brian.starkey@arm.com Cc: Chen Feng puck.chen@hisilicon.com Cc: Chen-Yu Tsai wens@csie.org Cc: Christian Gmeiner christian.gmeiner@gmail.com Cc: "Christian König" christian.koenig@amd.com Cc: Chun-Kuang Hu chunkuang.hu@kernel.org Cc: Edmund Dea edmund.j.dea@intel.com Cc: Eric Anholt eric@anholt.net Cc: Fabio Estevam festevam@gmail.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Haneen Mohammed hamohammed.sa@gmail.com Cc: Hans de Goede hdegoede@redhat.com Cc: "Heiko Stübner" heiko@sntech.de Cc: Huang Rui ray.huang@amd.com Cc: Hyun Kwon hyun.kwon@xilinx.com Cc: Inki Dae inki.dae@samsung.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Jernej Skrabec jernej.skrabec@siol.net Cc: Jerome Brunet jbrunet@baylibre.com Cc: Joel Stanley joel@jms.id.au Cc: John Stultz john.stultz@linaro.org Cc: Jonas Karlman jonas@kwiboo.se Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Joonyoung Shim jy0922.shim@samsung.com Cc: Jyri Sarha jyri.sarha@iki.fi Cc: Kevin Hilman khilman@baylibre.com Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com Cc: Kyungmin Park kyungmin.park@samsung.com Cc: Laurent Pinchart Laurent.pinchart@ideasonboard.com Cc: Linus Walleij linus.walleij@linaro.org Cc: Liviu Dudau liviu.dudau@arm.com Cc: Lucas Stach l.stach@pengutronix.de Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Marek Vasut marex@denx.de Cc: Martin Blumenstingl martin.blumenstingl@googlemail.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Maxime Coquelin mcoquelin.stm32@gmail.com Cc: Maxime Ripard mripard@kernel.org Cc: Melissa Wen melissa.srw@gmail.com Cc: Neil Armstrong narmstrong@baylibre.com Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: NXP Linux Team linux-imx@nxp.com Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: Patrik Jakobsson patrik.r.jakobsson@gmail.com Cc: Paul Cercueil paul@crapouillou.net Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pengutronix Kernel Team kernel@pengutronix.de Cc: Philippe Cornu philippe.cornu@foss.st.com Cc: Philipp Zabel p.zabel@pengutronix.de Cc: Qiang Yu yuq825@gmail.com Cc: Rob Clark robdclark@gmail.com Cc: Robert Foss robert.foss@linaro.org Cc: Rob Herring robh@kernel.org Cc: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Roland Scheidegger sroland@vmware.com Cc: Russell King linux@armlinux.org.uk Cc: Sam Ravnborg sam@ravnborg.org Cc: Sandy Huang hjc@rock-chips.com Cc: Sascha Hauer s.hauer@pengutronix.de Cc: Sean Paul sean@poorly.run Cc: Seung-Woo Kim sw0312.kim@samsung.com Cc: Shawn Guo shawnguo@kernel.org Cc: Simon Ser contact@emersion.fr Cc: Stefan Agner stefan@agner.ch Cc: Steven Price steven.price@arm.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thierry Reding thierry.reding@gmail.com Cc: Tian Tao tiantao6@hisilicon.com Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Tomi Valkeinen tomba@kernel.org Cc: VMware Graphics linux-graphics-maintainer@vmware.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: Xinwei Kong kong.kongxinwei@hisilicon.com Cc: Yannick Fertre yannick.fertre@foss.st.com Cc: Zack Rusin zackr@vmware.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Maxime Ripard maxime@cerno.tech
Changes from v3:
- Roll back to the v2
- Add Simon and Pekka in Cc
Changes from v2:
- Take into account the feedback from Laurent and Lidiu to no longer force generic properties, but prefix vendor-specific properties with the vendor name
Changes from v1:
- Typos and wording reported by Daniel and Alex
Documentation/gpu/drm-kms.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..c28b464dd397 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -463,6 +463,25 @@ KMS Properties This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections.
+Requirements +------------
+KMS drivers might need to add extra properties to support new features. +Each new property introduced in a driver need to meet a few +requirements, in addition to the one mentioned above.:
+- It must be standardized, with some documentation to describe how the
- property can be used.
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Property Types and Blob Property Support
Hi,
Regarding properties, we have a “case study example” related in a certain way to this documentation update :-)
The use case: on a front desk at an exhibition, there is a welcome screen you can touch for searching various information. When this welcome screen is in idle, a small logo is displayed at its center (around 20% of the fullscreen). The logo has a white background color. We want to reduce the ddr usage for lowering the power (the board is battery powered) so the idea is to use a white background color around this logo, produced by the drm CRTC so the image in ddr is only the size of the logo.
Reading the thread https://lists.freedesktop.org/archives/dri-devel/2019-October/239733.html dissuade us from coding a generic solution, so we started to implement a "STM_" private background color property, it works... but we are not at all convince this is the right way and we clearly prefer mainline/generic sw for both kernel & userland.
So now, what are our options... well, this v4 documentation update is I think clear enough: we have to document + provide a generic helper in the core code (similar to the original patch) + update IGT test, right?
Thanks Philippe :-)
Note: It is really a pleasure to read such interesting thread, exposing the “complexity” of our job, dealing with various hw and sw... thank you to all of you.
On Thu, Jun 17, 2021 at 05:38:36PM +0200, Philippe CORNU wrote:
On 6/16/21 4:38 PM, Maxime Ripard wrote:
New KMS properties come with a bunch of requirements to avoid each driver from running their own, inconsistent, set of properties, eventually leading to issues like property conflicts, inconsistencies between drivers and semantics, etc.
Let's document what we expect.
Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Alexandre Torgue alexandre.torgue@foss.st.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Alison Wang alison.wang@nxp.com Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Andrew Jeffery andrew@aj.id.au Cc: Andrzej Hajda a.hajda@samsung.com Cc: Anitha Chrisanthus anitha.chrisanthus@intel.com Cc: Benjamin Gaignard benjamin.gaignard@linaro.org Cc: Ben Skeggs bskeggs@redhat.com Cc: Boris Brezillon bbrezillon@kernel.org Cc: Brian Starkey brian.starkey@arm.com Cc: Chen Feng puck.chen@hisilicon.com Cc: Chen-Yu Tsai wens@csie.org Cc: Christian Gmeiner christian.gmeiner@gmail.com Cc: "Christian König" christian.koenig@amd.com Cc: Chun-Kuang Hu chunkuang.hu@kernel.org Cc: Edmund Dea edmund.j.dea@intel.com Cc: Eric Anholt eric@anholt.net Cc: Fabio Estevam festevam@gmail.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Haneen Mohammed hamohammed.sa@gmail.com Cc: Hans de Goede hdegoede@redhat.com Cc: "Heiko Stübner" heiko@sntech.de Cc: Huang Rui ray.huang@amd.com Cc: Hyun Kwon hyun.kwon@xilinx.com Cc: Inki Dae inki.dae@samsung.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Jernej Skrabec jernej.skrabec@siol.net Cc: Jerome Brunet jbrunet@baylibre.com Cc: Joel Stanley joel@jms.id.au Cc: John Stultz john.stultz@linaro.org Cc: Jonas Karlman jonas@kwiboo.se Cc: Jonathan Hunter jonathanh@nvidia.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Joonyoung Shim jy0922.shim@samsung.com Cc: Jyri Sarha jyri.sarha@iki.fi Cc: Kevin Hilman khilman@baylibre.com Cc: Kieran Bingham kieran.bingham+renesas@ideasonboard.com Cc: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com Cc: Kyungmin Park kyungmin.park@samsung.com Cc: Laurent Pinchart Laurent.pinchart@ideasonboard.com Cc: Linus Walleij linus.walleij@linaro.org Cc: Liviu Dudau liviu.dudau@arm.com Cc: Lucas Stach l.stach@pengutronix.de Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Marek Vasut marex@denx.de Cc: Martin Blumenstingl martin.blumenstingl@googlemail.com Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Maxime Coquelin mcoquelin.stm32@gmail.com Cc: Maxime Ripard mripard@kernel.org Cc: Melissa Wen melissa.srw@gmail.com Cc: Neil Armstrong narmstrong@baylibre.com Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: NXP Linux Team linux-imx@nxp.com Cc: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Cc: Patrik Jakobsson patrik.r.jakobsson@gmail.com Cc: Paul Cercueil paul@crapouillou.net Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Pengutronix Kernel Team kernel@pengutronix.de Cc: Philippe Cornu philippe.cornu@foss.st.com Cc: Philipp Zabel p.zabel@pengutronix.de Cc: Qiang Yu yuq825@gmail.com Cc: Rob Clark robdclark@gmail.com Cc: Robert Foss robert.foss@linaro.org Cc: Rob Herring robh@kernel.org Cc: Rodrigo Siqueira rodrigosiqueiramelo@gmail.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Roland Scheidegger sroland@vmware.com Cc: Russell King linux@armlinux.org.uk Cc: Sam Ravnborg sam@ravnborg.org Cc: Sandy Huang hjc@rock-chips.com Cc: Sascha Hauer s.hauer@pengutronix.de Cc: Sean Paul sean@poorly.run Cc: Seung-Woo Kim sw0312.kim@samsung.com Cc: Shawn Guo shawnguo@kernel.org Cc: Simon Ser contact@emersion.fr Cc: Stefan Agner stefan@agner.ch Cc: Steven Price steven.price@arm.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thierry Reding thierry.reding@gmail.com Cc: Tian Tao tiantao6@hisilicon.com Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Tomi Valkeinen tomba@kernel.org Cc: VMware Graphics linux-graphics-maintainer@vmware.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: Xinwei Kong kong.kongxinwei@hisilicon.com Cc: Yannick Fertre yannick.fertre@foss.st.com Cc: Zack Rusin zackr@vmware.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Maxime Ripard maxime@cerno.tech
Changes from v3:
- Roll back to the v2
- Add Simon and Pekka in Cc
Changes from v2:
- Take into account the feedback from Laurent and Lidiu to no longer force generic properties, but prefix vendor-specific properties with the vendor name
Changes from v1:
- Typos and wording reported by Daniel and Alex
Documentation/gpu/drm-kms.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..c28b464dd397 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -463,6 +463,25 @@ KMS Properties This section of the documentation is primarily aimed at user-space developers. For the driver APIs, see the other sections. +Requirements +------------
+KMS drivers might need to add extra properties to support new features. +Each new property introduced in a driver need to meet a few +requirements, in addition to the one mentioned above.:
+- It must be standardized, with some documentation to describe how the
- property can be used.
+- It must provide a generic helper in the core code to register that
- property on the object it attaches to.
+- Its content must be decoded by the core and provided in the object's
- associated state structure. That includes anything drivers might want to
- precompute, like :c:type:`struct drm_clip_rect <drm_clip_rect>` for planes.
+- An IGT test must be submitted where reasonable.
Property Types and Blob Property Support
Hi,
Regarding properties, we have a “case study example” related in a certain way to this documentation update :-)
The use case: on a front desk at an exhibition, there is a welcome screen you can touch for searching various information. When this welcome screen is in idle, a small logo is displayed at its center (around 20% of the fullscreen). The logo has a white background color. We want to reduce the ddr usage for lowering the power (the board is battery powered) so the idea is to use a white background color around this logo, produced by the drm CRTC so the image in ddr is only the size of the logo.
Reading the thread https://lists.freedesktop.org/archives/dri-devel/2019-October/239733.html dissuade us from coding a generic solution, so we started to implement a "STM_" private background color property, it works... but we are not at all convince this is the right way and we clearly prefer mainline/generic sw for both kernel & userland.
So now, what are our options... well, this v4 documentation update is I think clear enough: we have to document + provide a generic helper in the core code (similar to the original patch) + update IGT test, right?
Yeah, also background color has been talked about for a while (lots of hw can do it), it's just that no one ever found a use-case to make the background somethign else than "black". There's a pile of drivers who could expose this, so definitely makes sense to have this generic. -Daniel
Thanks Philippe :-)
Note: It is really a pleasure to read such interesting thread, exposing the “complexity” of our job, dealing with various hw and sw... thank you to all of you.
dri-devel@lists.freedesktop.org
-
Daniel Vetter -
Maxime Ripard -
Pekka Paalanen -
Philippe CORNU