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 <max...@cerno.tech> 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.bell...@bootlin.com> > > Cc: Alexandre Torgue <alexandre.tor...@foss.st.com> > > Cc: Alex Deucher <alexander.deuc...@amd.com> > > Cc: Alison Wang <alison.w...@nxp.com> > > Cc: Alyssa Rosenzweig <alyssa.rosenzw...@collabora.com> > > Cc: Andrew Jeffery <and...@aj.id.au> > > Cc: Andrzej Hajda <a.ha...@samsung.com> > > Cc: Anitha Chrisanthus <anitha.chrisant...@intel.com> > > Cc: Benjamin Gaignard <benjamin.gaign...@linaro.org> > > Cc: Ben Skeggs <bske...@redhat.com> > > Cc: Boris Brezillon <bbrezil...@kernel.org> > > Cc: Brian Starkey <brian.star...@arm.com> > > Cc: Chen Feng <puck.c...@hisilicon.com> > > Cc: Chen-Yu Tsai <w...@csie.org> > > Cc: Christian Gmeiner <christian.gmei...@gmail.com> > > Cc: "Christian König" <christian.koe...@amd.com> > > Cc: Chun-Kuang Hu <chunkuang...@kernel.org> > > Cc: Edmund Dea <edmund.j....@intel.com> > > Cc: Eric Anholt <e...@anholt.net> > > Cc: Fabio Estevam <feste...@gmail.com> > > Cc: Gerd Hoffmann <kra...@redhat.com> > > Cc: Haneen Mohammed <hamohammed...@gmail.com> > > Cc: Hans de Goede <hdego...@redhat.com> > > Cc: "Heiko Stübner" <he...@sntech.de> > > Cc: Huang Rui <ray.hu...@amd.com> > > Cc: Hyun Kwon <hyun.k...@xilinx.com> > > Cc: Inki Dae <inki....@samsung.com> > > Cc: Jani Nikula <jani.nik...@linux.intel.com> > > Cc: Jernej Skrabec <jernej.skra...@siol.net> > > Cc: Jerome Brunet <jbru...@baylibre.com> > > Cc: Joel Stanley <j...@jms.id.au> > > Cc: John Stultz <john.stu...@linaro.org> > > Cc: Jonas Karlman <jo...@kwiboo.se> > > Cc: Jonathan Hunter <jonath...@nvidia.com> > > Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com> > > Cc: Joonyoung Shim <jy0922.s...@samsung.com> > > Cc: Jyri Sarha <jyri.sa...@iki.fi> > > Cc: Kevin Hilman <khil...@baylibre.com> > > Cc: Kieran Bingham <kieran.bingham+rene...@ideasonboard.com> > > Cc: Krzysztof Kozlowski <krzysztof.kozlow...@canonical.com> > > Cc: Kyungmin Park <kyungmin.p...@samsung.com> > > Cc: Laurent Pinchart <laurent.pinch...@ideasonboard.com> > > Cc: Linus Walleij <linus.wall...@linaro.org> > > Cc: Liviu Dudau <liviu.du...@arm.com> > > Cc: Lucas Stach <l.st...@pengutronix.de> > > Cc: Ludovic Desroches <ludovic.desroc...@microchip.com> > > Cc: Marek Vasut <ma...@denx.de> > > Cc: Martin Blumenstingl <martin.blumensti...@googlemail.com> > > Cc: Matthias Brugger <matthias....@gmail.com> > > Cc: Maxime Coquelin <mcoquelin.st...@gmail.com> > > Cc: Maxime Ripard <mrip...@kernel.org> > > Cc: Melissa Wen <melissa....@gmail.com> > > Cc: Neil Armstrong <narmstr...@baylibre.com> > > Cc: Nicolas Ferre <nicolas.fe...@microchip.com> > > Cc: "Noralf Trønnes" <nor...@tronnes.org> > > Cc: NXP Linux Team <linux-...@nxp.com> > > Cc: Oleksandr Andrushchenko <oleksandr_andrushche...@epam.com> > > Cc: Patrik Jakobsson <patrik.r.jakobs...@gmail.com> > > Cc: Paul Cercueil <p...@crapouillou.net> > > Cc: Pekka Paalanen <pekka.paala...@collabora.com> > > Cc: Pengutronix Kernel Team <ker...@pengutronix.de> > > Cc: Philippe Cornu <philippe.co...@foss.st.com> > > Cc: Philipp Zabel <p.za...@pengutronix.de> > > Cc: Qiang Yu <yuq...@gmail.com> > > Cc: Rob Clark <robdcl...@gmail.com> > > Cc: Robert Foss <robert.f...@linaro.org> > > Cc: Rob Herring <r...@kernel.org> > > Cc: Rodrigo Siqueira <rodrigosiqueiram...@gmail.com> > > Cc: Rodrigo Vivi <rodrigo.v...@intel.com> > > Cc: Roland Scheidegger <srol...@vmware.com> > > Cc: Russell King <li...@armlinux.org.uk> > > Cc: Sam Ravnborg <s...@ravnborg.org> > > Cc: Sandy Huang <h...@rock-chips.com> > > Cc: Sascha Hauer <s.ha...@pengutronix.de> > > Cc: Sean Paul <s...@poorly.run> > > Cc: Seung-Woo Kim <sw0312....@samsung.com> > > Cc: Shawn Guo <shawn...@kernel.org> > > Cc: Simon Ser <cont...@emersion.fr> > > Cc: Stefan Agner <ste...@agner.ch> > > Cc: Steven Price <steven.pr...@arm.com> > > Cc: Sumit Semwal <sumit.sem...@linaro.org> > > Cc: Thierry Reding <thierry.red...@gmail.com> > > Cc: Tian Tao <tiant...@hisilicon.com> > > Cc: Tomeu Vizoso <tomeu.viz...@collabora.com> > > Cc: Tomi Valkeinen <to...@kernel.org> > > Cc: VMware Graphics <linux-graphics-maintai...@vmware.com> > > Cc: Xinliang Liu <xinliang....@linaro.org> > > Cc: Xinwei Kong <kong.kongxin...@hisilicon.com> > > Cc: Yannick Fertre <yannick.fer...@foss.st.com> > > Cc: Zack Rusin <za...@vmware.com> > > Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch> > > Signed-off-by: Maxime Ripard <max...@cerno.tech> > > > > --- > > > > 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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