[PATCH v4] Documentation: gpu: Mention the requirements for new properties

Thu Jun 17 15:38:36 UTC 2021

On 6/16/21 4:38 PM, 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 at bootlin.com>
> Cc: Alexandre Torgue <alexandre.torgue at foss.st.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Alison Wang <alison.wang at nxp.com>
> Cc: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
> Cc: Andrew Jeffery <andrew at aj.id.au>
> Cc: Andrzej Hajda <a.hajda at samsung.com>
> Cc: Anitha Chrisanthus <anitha.chrisanthus at intel.com>
> Cc: Benjamin Gaignard <benjamin.gaignard at linaro.org>
> Cc: Ben Skeggs <bskeggs at redhat.com>
> Cc: Boris Brezillon <bbrezillon at kernel.org>
> Cc: Brian Starkey <brian.starkey at arm.com>
> Cc: Chen Feng <puck.chen at hisilicon.com>
> Cc: Chen-Yu Tsai <wens at csie.org>
> Cc: Christian Gmeiner <christian.gmeiner at gmail.com>
> Cc: "Christian König" <christian.koenig at amd.com>
> Cc: Chun-Kuang Hu <chunkuang.hu at kernel.org>
> Cc: Edmund Dea <edmund.j.dea at intel.com>
> Cc: Eric Anholt <eric at anholt.net>
> Cc: Fabio Estevam <festevam at gmail.com>
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Haneen Mohammed <hamohammed.sa at gmail.com>
> Cc: Hans de Goede <hdegoede at redhat.com>
> Cc: "Heiko Stübner" <heiko at sntech.de>
> Cc: Huang Rui <ray.huang at amd.com>
> Cc: Hyun Kwon <hyun.kwon at xilinx.com>
> Cc: Inki Dae <inki.dae at samsung.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Jernej Skrabec <jernej.skrabec at siol.net>
> Cc: Jerome Brunet <jbrunet at baylibre.com>
> Cc: Joel Stanley <joel at jms.id.au>
> Cc: John Stultz <john.stultz at linaro.org>
> Cc: Jonas Karlman <jonas at kwiboo.se>
> Cc: Jonathan Hunter <jonathanh at nvidia.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Joonyoung Shim <jy0922.shim at samsung.com>
> Cc: Jyri Sarha <jyri.sarha at iki.fi>
> Cc: Kevin Hilman <khilman at baylibre.com>
> Cc: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
> Cc: Krzysztof Kozlowski <krzysztof.kozlowski at canonical.com>
> Cc: Kyungmin Park <kyungmin.park at samsung.com>
> Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
> Cc: Linus Walleij <linus.walleij at linaro.org>
> Cc: Liviu Dudau <liviu.dudau at arm.com>
> Cc: Lucas Stach <l.stach at pengutronix.de>
> Cc: Ludovic Desroches <ludovic.desroches at microchip.com>
> Cc: Marek Vasut <marex at denx.de>
> Cc: Martin Blumenstingl <martin.blumenstingl at googlemail.com>
> Cc: Matthias Brugger <matthias.bgg at gmail.com>
> Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Melissa Wen <melissa.srw at gmail.com>
> Cc: Neil Armstrong <narmstrong at baylibre.com>
> Cc: Nicolas Ferre <nicolas.ferre at microchip.com>
> Cc: "Noralf Trønnes" <noralf at tronnes.org>
> Cc: NXP Linux Team <linux-imx at nxp.com>
> Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko at epam.com>
> Cc: Patrik Jakobsson <patrik.r.jakobsson at gmail.com>
> Cc: Paul Cercueil <paul at crapouillou.net>
> Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
> Cc: Pengutronix Kernel Team <kernel at pengutronix.de>
> Cc: Philippe Cornu <philippe.cornu at foss.st.com>
> Cc: Philipp Zabel <p.zabel at pengutronix.de>
> Cc: Qiang Yu <yuq825 at gmail.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Robert Foss <robert.foss at linaro.org>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Roland Scheidegger <sroland at vmware.com>
> Cc: Russell King <linux at armlinux.org.uk>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: Sandy Huang <hjc at rock-chips.com>
> Cc: Sascha Hauer <s.hauer at pengutronix.de>
> Cc: Sean Paul <sean at poorly.run>
> Cc: Seung-Woo Kim <sw0312.kim at samsung.com>
> Cc: Shawn Guo <shawnguo at kernel.org>
> Cc: Simon Ser <contact at emersion.fr>
> Cc: Stefan Agner <stefan at agner.ch>
> Cc: Steven Price <steven.price at arm.com>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: Thierry Reding <thierry.reding at gmail.com>
> Cc: Tian Tao <tiantao6 at hisilicon.com>
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> Cc: Tomi Valkeinen <tomba at kernel.org>
> Cc: VMware Graphics <linux-graphics-maintainer at vmware.com>
> Cc: Xinliang Liu <xinliang.liu at linaro.org>
> Cc: Xinwei Kong <kong.kongxinwei at hisilicon.com>
> Cc: Yannick Fertre <yannick.fertre at foss.st.com>
> Cc: Zack Rusin <zackr at vmware.com>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> Signed-off-by: Maxime Ripard <maxime at 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.
> +
> +- 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.
> +
>   Property Types and Blob Property Support
>   ----------------------------------------
>   
> 

Hi,

Regarding properties, we have a “case study example” related in a 
certain way to this documentation update :-)

The use case: on a front desk at an exhibition, there is a welcome 
screen you can touch for searching various information. When this 
welcome screen is in idle, a small logo is displayed at its center 
(around 20% of the fullscreen). The logo has a white background color. 
We want to reduce the ddr usage for lowering the power (the board is 
battery powered) so the idea is to use a white background color around 
this logo, produced by the drm CRTC so the image in ddr is only the size 
of the logo.

Reading the thread 
https://lists.freedesktop.org/archives/dri-devel/2019-October/239733.html 
dissuade us from coding a generic solution, so we started to implement a 
"STM_" private background color property, it works... but we are not at 
all convince this is the right way and we clearly prefer 
mainline/generic sw for both kernel & userland.

So now, what are our options... well, this v4 documentation update is I 
think clear enough: we have to document + provide a generic helper in 
the core code (similar to the original patch) + update IGT test, right?

Thanks
Philippe :-)

Note: It is really a pleasure to read such interesting thread, exposing 
the “complexity” of our job, dealing with various hw and sw... thank you 
to all of you.