Hi Laurent,
On Mon, May 24, 2021 at 07:04:43AM +0300, Laurent Pinchart wrote:
Hi Maxime,
Thank you for the patch.
On Thu, May 20, 2021 at 04:24:35PM +0200, 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: 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: 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 v2:
- 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
s/need/needs/
+requirements, in addition to the one mentioned above.:
s/above./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.
Does this effectively mean that we completely forbid driver-specific properties ? While I agree that we should strive for standardization, there are two issues that worry me. The first one is simple, we may need to control features that would be very device-specific, and standardizing properties doesn't seem to make much sense in that case.
I'd say that we should make it clear in that case that it's driver-specific.
The second issue relates to properties that could be applicable to multiple devices, but for which we have a single driver. Designing a standard with a single data point usually leads to a bad design. I'm not sure how to handle this correctly though, as we certainly don't want this to be taken as an excuse to create driver-specific properties when generic properties would make sense.
The discussion that made us create that patch was about this property: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/driv...
It's all kind of bad: - It kind of conflicts with the generic Colorspace property - It's not really a colorspace (Not that "Colorspace" is either) - It could have been made generic from the start - We don't have any knowledge on who uses it and why, so it's difficult to rework
This was introduced before we had any kind of rule or documentation on the UAPI though, so there's no-one to blame really but we don't really want to have something like that happen again.
I agree that doing something generic from the beginning can be difficult, but this is some userspace API that we will have to carry around forever, so it's worth it I guess?
You have a point on the vendor properties though. Maybe we can require a vendor prefix for those? It would reduce the risk of a conflict.
Maxime