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 <[email protected]> > > > Cc: Alexandre Torgue <[email protected]> > > > Cc: Alex Deucher <[email protected]> > > > Cc: Alison Wang <[email protected]> > > > Cc: Alyssa Rosenzweig <[email protected]> > > > Cc: Andrew Jeffery <[email protected]> > > > Cc: Andrzej Hajda <[email protected]> > > > Cc: Anitha Chrisanthus <[email protected]> > > > Cc: Benjamin Gaignard <[email protected]> > > > Cc: Ben Skeggs <[email protected]> > > > Cc: Boris Brezillon <[email protected]> > > > Cc: Brian Starkey <[email protected]> > > > Cc: Chen Feng <[email protected]> > > > Cc: Chen-Yu Tsai <[email protected]> > > > Cc: Christian Gmeiner <[email protected]> > > > Cc: "Christian König" <[email protected]> > > > Cc: Chun-Kuang Hu <[email protected]> > > > Cc: Edmund Dea <[email protected]> > > > Cc: Eric Anholt <[email protected]> > > > Cc: Fabio Estevam <[email protected]> > > > Cc: Gerd Hoffmann <[email protected]> > > > Cc: Haneen Mohammed <[email protected]> > > > Cc: Hans de Goede <[email protected]> > > > Cc: "Heiko Stübner" <[email protected]> > > > Cc: Huang Rui <[email protected]> > > > Cc: Hyun Kwon <[email protected]> > > > Cc: Inki Dae <[email protected]> > > > Cc: Jani Nikula <[email protected]> > > > Cc: Jernej Skrabec <[email protected]> > > > Cc: Jerome Brunet <[email protected]> > > > Cc: Joel Stanley <[email protected]> > > > Cc: John Stultz <[email protected]> > > > Cc: Jonas Karlman <[email protected]> > > > Cc: Jonathan Hunter <[email protected]> > > > Cc: Joonas Lahtinen <[email protected]> > > > Cc: Joonyoung Shim <[email protected]> > > > Cc: Jyri Sarha <[email protected]> > > > Cc: Kevin Hilman <[email protected]> > > > Cc: Kieran Bingham <[email protected]> > > > Cc: Krzysztof Kozlowski <[email protected]> > > > Cc: Kyungmin Park <[email protected]> > > > Cc: Laurent Pinchart <[email protected]> > > > Cc: Linus Walleij <[email protected]> > > > Cc: Liviu Dudau <[email protected]> > > > Cc: Lucas Stach <[email protected]> > > > Cc: Ludovic Desroches <[email protected]> > > > Cc: Marek Vasut <[email protected]> > > > Cc: Martin Blumenstingl <[email protected]> > > > Cc: Matthias Brugger <[email protected]> > > > Cc: Maxime Coquelin <[email protected]> > > > Cc: Maxime Ripard <[email protected]> > > > Cc: Melissa Wen <[email protected]> > > > Cc: Neil Armstrong <[email protected]> > > > Cc: Nicolas Ferre <[email protected]> > > > Cc: "Noralf Trønnes" <[email protected]> > > > Cc: NXP Linux Team <[email protected]> > > > Cc: Oleksandr Andrushchenko <[email protected]> > > > Cc: Patrik Jakobsson <[email protected]> > > > Cc: Paul Cercueil <[email protected]> > > > Cc: Pengutronix Kernel Team <[email protected]> > > > Cc: Philippe Cornu <[email protected]> > > > Cc: Philipp Zabel <[email protected]> > > > Cc: Qiang Yu <[email protected]> > > > Cc: Rob Clark <[email protected]> > > > Cc: Robert Foss <[email protected]> > > > Cc: Rob Herring <[email protected]> > > > Cc: Rodrigo Siqueira <[email protected]> > > > Cc: Rodrigo Vivi <[email protected]> > > > Cc: Roland Scheidegger <[email protected]> > > > Cc: Russell King <[email protected]> > > > Cc: Sam Ravnborg <[email protected]> > > > Cc: Sandy Huang <[email protected]> > > > Cc: Sascha Hauer <[email protected]> > > > Cc: Sean Paul <[email protected]> > > > Cc: Seung-Woo Kim <[email protected]> > > > Cc: Shawn Guo <[email protected]> > > > Cc: Stefan Agner <[email protected]> > > > Cc: Steven Price <[email protected]> > > > Cc: Sumit Semwal <[email protected]> > > > Cc: Thierry Reding <[email protected]> > > > Cc: Tian Tao <[email protected]> > > > Cc: Tomeu Vizoso <[email protected]> > > > Cc: Tomi Valkeinen <[email protected]> > > > Cc: VMware Graphics <[email protected]> > > > Cc: Xinliang Liu <[email protected]> > > > Cc: Xinwei Kong <[email protected]> > > > Cc: Yannick Fertre <[email protected]> > > > Cc: Zack Rusin <[email protected]> > > > Reviewed-by: Daniel Vetter <[email protected]> > > > Signed-off-by: Maxime Ripard <[email protected]> > > > > > > --- > > > > > > 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
