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