On Tue, 6 Jul 2021 10:52:02 +0200 Maxime Ripard <maxime@xxxxxxxxxx> wrote: > 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. Hi, yes, exactly that is why fbdev/fbcon should reset the properties to their initial values. You would not want userspace inheriting a different KMS state with vs. without fbcon when it starts. Retrieving the current KMS state is useless if the current KMS state is somehow wonky and the application does not understand that specific KMS property that is wonky. It cannot set the property to any value other than it already had without user intervention. I'd say fbcon causing all KMS state to be reset is a quality of life thing. It's possible to live without by rebooting, but it would certainly make at least developers' and testers' life easier until we get the real "reset KMS" knob (which fbcon could then use too). Besides, even if it is broken for userspace to rely on the KMS state set by fbcon/fbdev, userspace is already doing that and not on purpose because new KMS properties get added in the kernel. I would bet that there is not a single userspace program that would actually set all KMS properties that drivers might expose. So they are depending on inherited KMS state, which could be left by driver initialization, by fbdev/fbcon, or by any other userspace. But yeah, this idea is something new, so don't let this discussion delay landing the docs. Thanks, pq
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