linux-kernel - Re: [PATCH v2 1/8] drm/connector: let drivers declare infoframes as unsupported

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Message-ID: <20250820-artichoke-silkworm-of-election-521b5e@houat>
Date: Wed, 20 Aug 2025 09:15:36 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Sandy Huang <hjc@...k-chips.com>, 
	Heiko Stübner <heiko@...ech.de>, Andy Yan <andy.yan@...k-chips.com>, Chen-Yu Tsai <wens@...e.org>, 
	Samuel Holland <samuel@...lland.org>, Dave Stevenson <dave.stevenson@...pberrypi.com>, 
	Maíra Canal <mcanal@...lia.com>, Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, 
	Liu Ying <victor.liu@....com>, Rob Clark <robin.clark@....qualcomm.com>, 
	Dmitry Baryshkov <lumag@...nel.org>, Abhinav Kumar <abhinav.kumar@...ux.dev>, 
	Jessica Zhang <jessica.zhang@....qualcomm.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, linux-sunxi@...ts.linux.dev, 
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v2 1/8] drm/connector: let drivers declare infoframes as
 unsupported

Hi,

On Tue, Aug 19, 2025 at 09:57:30PM +0300, Dmitry Baryshkov wrote:
> Currently DRM framework expects that the HDMI connector driver supports
> all infoframe types: it generates the data as required and calls into
> the driver to program all of them, letting the driver to soft-fail if
> the infoframe is unsupported. This has a major drawback on userspace
> API: the framework also registers debugfs files for all Infoframe types,
> possibly surprising the users when infoframe is visible in the debugfs
> file, but it is not visible on the wire.
> 
> Let drivers declare that they support only a subset of infoframes,
> creating a more consistent interface.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>

I'm not really convinced. Infoframes aren't really something you should
ignore, AVI is effectively mandatory, HDMI kind of is too, AUDIO is if
audio support is enabled, DRM is mandatory if HDR is used.

SPD is indeed optional though.

So, it's really dynamic in essence, and not really something we should
expect drivers to ignore.

I do acknowledge that a lot of drivers just silently ignore the
infoframes they don't support at the moment, which isn't great either.

Maybe we should standardize and document what drivers should do when
they don't support a given infoframe type?

Something like return EOPNOTSUPP if you don't support it, and we warn in
the core if we get one for a mandatory infoframe?

Maxime

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