Hi Maxime, On Tue, May 25, 2021 at 12:39:40PM +0200, Maxime Ripard wrote: > On Mon, May 24, 2021 at 07:04:43AM +0300, Laurent Pinchart wrote: > > 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@xxxxxxxxxxx> > > > Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx> > > > Cc: Alex Deucher <alexander.deucher@xxxxxxx> > > > Cc: Alison Wang <alison.wang@xxxxxxx> > > > Cc: Alyssa Rosenzweig <alyssa.rosenzweig@xxxxxxxxxxxxx> > > > Cc: Andrew Jeffery <andrew@xxxxxxxx> > > > Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx> > > > Cc: Anitha Chrisanthus <anitha.chrisanthus@xxxxxxxxx> > > > Cc: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxx> > > > Cc: Ben Skeggs <bskeggs@xxxxxxxxxx> > > > Cc: Boris Brezillon <bbrezillon@xxxxxxxxxx> > > > Cc: Brian Starkey <brian.starkey@xxxxxxx> > > > Cc: Chen Feng <puck.chen@xxxxxxxxxxxxx> > > > Cc: Chen-Yu Tsai <wens@xxxxxxxx> > > > Cc: Christian Gmeiner <christian.gmeiner@xxxxxxxxx> > > > Cc: "Christian König" <christian.koenig@xxxxxxx> > > > Cc: Chun-Kuang Hu <chunkuang.hu@xxxxxxxxxx> > > > Cc: Edmund Dea <edmund.j.dea@xxxxxxxxx> > > > Cc: Eric Anholt <eric@xxxxxxxxxx> > > > Cc: Fabio Estevam <festevam@xxxxxxxxx> > > > Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> > > > Cc: Haneen Mohammed <hamohammed.sa@xxxxxxxxx> > > > Cc: Hans de Goede <hdegoede@xxxxxxxxxx> > > > Cc: "Heiko Stübner" <heiko@xxxxxxxxx> > > > Cc: Huang Rui <ray.huang@xxxxxxx> > > > Cc: Hyun Kwon <hyun.kwon@xxxxxxxxxx> > > > Cc: Inki Dae <inki.dae@xxxxxxxxxxx> > > > Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> > > > Cc: Jernej Skrabec <jernej.skrabec@xxxxxxxx> > > > Cc: Jerome Brunet <jbrunet@xxxxxxxxxxxx> > > > Cc: Joel Stanley <joel@xxxxxxxxx> > > > Cc: John Stultz <john.stultz@xxxxxxxxxx> > > > Cc: Jonas Karlman <jonas@xxxxxxxxx> > > > Cc: Jonathan Hunter <jonathanh@xxxxxxxxxx> > > > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > > > Cc: Joonyoung Shim <jy0922.shim@xxxxxxxxxxx> > > > Cc: Jyri Sarha <jyri.sarha@xxxxxx> > > > Cc: Kevin Hilman <khilman@xxxxxxxxxxxx> > > > Cc: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx> > > > Cc: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxx> > > > Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > > Cc: Laurent Pinchart <Laurent.pinchart@xxxxxxxxxxxxxxxx> > > > Cc: Linus Walleij <linus.walleij@xxxxxxxxxx> > > > Cc: Liviu Dudau <liviu.dudau@xxxxxxx> > > > Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx> > > > Cc: Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx> > > > Cc: Marek Vasut <marex@xxxxxxx> > > > Cc: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx> > > > Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx> > > > Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx> > > > Cc: Maxime Ripard <mripard@xxxxxxxxxx> > > > Cc: Melissa Wen <melissa.srw@xxxxxxxxx> > > > Cc: Neil Armstrong <narmstrong@xxxxxxxxxxxx> > > > Cc: Nicolas Ferre <nicolas.ferre@xxxxxxxxxxxxx> > > > Cc: "Noralf Trønnes" <noralf@xxxxxxxxxxx> > > > Cc: NXP Linux Team <linux-imx@xxxxxxx> > > > Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> > > > Cc: Patrik Jakobsson <patrik.r.jakobsson@xxxxxxxxx> > > > Cc: Paul Cercueil <paul@xxxxxxxxxxxxxxx> > > > Cc: Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx> > > > Cc: Philippe Cornu <philippe.cornu@xxxxxxxxxxx> > > > Cc: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > > > Cc: Qiang Yu <yuq825@xxxxxxxxx> > > > Cc: Rob Clark <robdclark@xxxxxxxxx> > > > Cc: Robert Foss <robert.foss@xxxxxxxxxx> > > > Cc: Rob Herring <robh@xxxxxxxxxx> > > > Cc: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx> > > > Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx> > > > Cc: Roland Scheidegger <sroland@xxxxxxxxxx> > > > Cc: Russell King <linux@xxxxxxxxxxxxxxx> > > > Cc: Sam Ravnborg <sam@xxxxxxxxxxxx> > > > Cc: Sandy Huang <hjc@xxxxxxxxxxxxxx> > > > Cc: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> > > > Cc: Sean Paul <sean@xxxxxxxxxx> > > > Cc: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx> > > > Cc: Shawn Guo <shawnguo@xxxxxxxxxx> > > > Cc: Stefan Agner <stefan@xxxxxxxx> > > > Cc: Steven Price <steven.price@xxxxxxx> > > > Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx> > > > Cc: Thierry Reding <thierry.reding@xxxxxxxxx> > > > Cc: Tian Tao <tiantao6@xxxxxxxxxxxxx> > > > Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx> > > > Cc: Tomi Valkeinen <tomba@xxxxxxxxxx> > > > Cc: VMware Graphics <linux-graphics-maintainer@xxxxxxxxxx> > > > Cc: Xinliang Liu <xinliang.liu@xxxxxxxxxx> > > > Cc: Xinwei Kong <kong.kongxinwei@xxxxxxxxxxxxx> > > > Cc: Yannick Fertre <yannick.fertre@xxxxxxxxxxx> > > > Cc: Zack Rusin <zackr@xxxxxxxxxx> > > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > > Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx> > > > > > > --- > > > > > > 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/drivers/gpu/drm/sti/sti_hdmi.c#n170 > > 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? It is, no disagreement about that. Pushing driver authors to explore standardization of properties is a good idea. As long as we have a pragmatic approach and allow vendor-specific properties when it makes sense, I'll have no concern. > 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. I like the idea of a vendor prefix. -- Regards, Laurent Pinchart
