[PATCH v6] Documentation: gpu: Mention the requirements for new properties

[Maxime Ripard]

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: 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: Pekka Paalanen <pekka.paalanen at collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Maxime Ripard <maxime at cerno.tech>

---

Changes from v5:
  - Typos fixes suggested by Pekka and Daniel
  - Added Pekka Reviewed-by

Changes from v4:
  - Changes suggested by Pekka

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 | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
index 87e5023e3f55..12e25119e563 100644
--- a/Documentation/gpu/drm-kms.rst
+++ b/Documentation/gpu/drm-kms.rst
@@ -463,6 +463,35 @@ 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 needs to meet a few requirements, in
+addition to the one mentioned above:
+
+* It must be standardized, documenting:
+
+  * The full, exact, name string;
+  * If the property is an enum, all the valid value name strings;
+  * What values are accepted, and what these values mean;
+  * What the property does and how it can be used;
+  * How the property might interact with other, existing properties.
+
+* 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 struct drm_clip_rect for planes.
+
+* Its initial state must match the behavior prior to the property
+  introduction. This might be a fixed value matching what the hardware
+  does, or it may be inherited from the state the firmware left the
+  system in during boot.
+
+* An IGT test must be submitted where reasonable.
+
 Property Types and Blob Property Support
 ----------------------------------------
 
-- 
2.31.1