Hi,

On Wed, Aug 20, 2025 at 12:52:44PM +0300, Dmitry Baryshkov wrote:

On Wed, Aug 20, 2025 at 09:15:36AM +0200, Maxime Ripard wrote:

quoted

Hi,

On Tue, Aug 19, 2025 at 09:57:30PM +0300, Dmitry Baryshkov wrote:

quoted

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 <redacted>

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.

Nevertheless, sun4i, innohdmi, adv7511, it6263 and rk3066 drivers
provide support only for the AVI infoframe.

Yes, but it's still something we shouldn't paper over. The spec mandates
it, if drivers want to deviate from it it's something we should warn
about, not silence.

sun4i is a good example, to me at least since I have the doc. The
hardware supports AVI, Audio, ACP, and SPD. HDR isn't supported, so DRM
isn't either. The only missing one is HDMI, but the documentation isn't
the best so it might still be supported. In short, it's a driver issue.

adv7511 supports AVI, Audio, ACP, SPD, ACP, and looks to have a
mechanism to send any infoframe as is. So, again, driver issue.

I couldn't find the other datasheet, but I'd be very surprised if it
wasn't the case for these too.

Some of them can be extended to support other infoframe kinds (e.g.
ADV7511 has two spare infoframes which can be used for HDMI and SPD).

quoted

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?

The chips might be generating infoframes internally. This series was
triggered by LT9611UXC, which does all HDMI work under the hood in the
firmware. See [1]. The series I posted hooks HDMI audio directly into
the bridge driver, but I'd really prefer to be able to use
drm_atomic_helper_connector_hdmi_hotplug(), especially if I ever get to
implementing CEC support for it.

ADV7511 likewise generates audio infoframe without Linux
help (audio-related fields are programmed, but it's not the
infoframe itself).

Implementing the write_infoframe hooks as a nop with a comment in those
case is totally reasonable to me.

I'd still like to document that drivers should only return 0 if they
programmed the infoframe, and -ENOTSUPP (and the core logging a warning)
otherwise.

That way, we would be able to differentiate between the legimitate
LT9611UXC case, and the "driver is broken" sun4i (and others) case.

Maxime