linux-kernel - Re: [PATCH v3 00/11] drm/connector: hdmi: limit infoframes per driver capabilities

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Message-ID: <CAPj87rOSb90S_TeA8Cu5kd-M8bbfiE0fvPzgr9Gr4e9_rfZeFQ@mail.gmail.com>
Date: Sun, 31 Aug 2025 15:46:25 +0200
From: Daniel Stone <daniel@...ishbar.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>, Maxime Ripard <mripard@...nel.org>, 
	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 v3 00/11] drm/connector: hdmi: limit infoframes per driver capabilities

Hi Dmitry,

On Sun, 31 Aug 2025 at 00:29, Dmitry Baryshkov
<dmitry.baryshkov@....qualcomm.com> wrote:
> On Sat, Aug 30, 2025 at 09:30:01AM +0200, Daniel Stone wrote:
> > I know that dw-hdmi-qp can support _any_ infoframe, by manually
> > packing it into the two GHDMI banks. So the supported set there is
> > 'all of the currently well-known ones, plus any two others, but only
> > two and not more'. I wonder if that has any effect on the interface
> > you were thinking about for userspace?
>
> I was mostly concerned with the existing debugfs interface (as it is
> also used e.g. for edid-decode, etc).
>
> It seems "everything + 2 spare" is more or less common (ADV7511, MSM
> HDMI also have those. I don't have at hand the proper datasheet for
> LT9611 (non-UXC one), but I think its InfoFrames are also more or less
> generic).  Maybe we should change debugfs integration to register the
> file when the frame is being enabled and removing it when it gets unset.

Oh right, that's really interesting.

> Then in the long run we can add 'slots' and allocate some of the frames
> to the slots. E.g. ADV7511 would get 'software AVI', 'software SPD',
> 'auto AUDIO' + 2 generic slots (and MPEG InfoFrame which can probably be
> salvaged as another generic one)). MSM HDMI would get 'software AVI',
> 'software AUDIO' + 2 generic slots (+MPEG + obsucre HDMI which I don't
> want to use). Then the framework might be able to prioritize whether to
> use generic slots for important data (as DRM HDR, HDMI) or less important
> (SPD).

Yeah, that sounds good! I wonder if we want to surface that from the
debugfs interface: maybe just files named 0..$numslots with the
content of the infoframes, one named 'slots' with the integer index,
which infoframe type it's currently carrying, and which types it's
capable of carrying. Then to preserve the current interface, symlinks
from the infoframe type name to the slot index.

Cheers,
Daniel