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@xxxxxxxxxx> 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: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx> > > 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: Simon Ser <contact@xxxxxxxxxxx> > > 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 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
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