Re: [PATCH v4 01/10] drm/connector: let drivers declare infoframes as unsupported

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On 03/10/2025 17:23, Maxime Ripard wrote:
> On Thu, Sep 25, 2025 at 05:55:06PM +0300, Dmitry Baryshkov wrote:
>>>> As we will be getting more and more features, some of the InfoFrames
>>>> or data packets will be 'good to have, but not required'.
>>>
>>> And drivers would be free to ignore those.
>>>
>>>>> So, no, sorry. That's still a no for me. Please stop sending that patch
>>>>
>>>> Oops :-)
>>>>
>>>>> unless we have a discussion about it and you convince me that it's
>>>>> actually something that we'd need.
>>>>
>>>> My main concern is that the drivers should not opt-out of the features.
>>>> E.g. if we start supporting ISRC packets or MPEG or NTSC VBI InfoFrames
>>>> (yes, stupid examples), it should not be required to go through all the
>>>> drivers, making sure that they disable those. Instead the DRM framework
>>>> should be able to make decisions like:
>>>>
>>>> - The driver supports SPD and the VSDB defines SPD, enable this
>>>>    InfoFrame (BTW, this needs to be done anyway, we should not be sending
>>>>    SPD if it's not defined in VSDB, if I read it correctly).
>>>>
>>>> - The driver hints that the pixel data has only 10 meaninful bits of
>>>>    data per component (e.g. out of 12 for DeepColor 36), the Sink has
>>>>    HF-VSDB, send HF-VSIF.
>>>>
>>>> - The driver has enabled 3D stereo mode, but it doesn't declare support
>>>>    for HF-VSIF. Send only H14b-VSIF.
>>>>
>>>> Similarly (no, I don't have these on my TODO list, these are just
>>>> examples):
>>>> - The driver defines support for NTSC VBI, register a VBI device.
>>>>
>>>> - The driver defines support for ISRC packets, register ISRC-related
>>>>    properties.
>>>>
>>>> - The driver defines support for MPEG Source InfoFrame, provide a way
>>>>    for media players to report frame type and bit rate.
>>>>
>>>> - The driver provides limited support for Extended HDR DM InfoFrames,
>>>>    select the correct frame type according to driver capabilities.
>>>>
>>>> Without the 'supported' information we should change atomic_check()
>>>> functions to set infoframe->set to false for all unsupported InfoFrames
>>>> _and_ go through all the drivers again each time we add support for a
>>>> feature (e.g. after adding HF-VSIF support).
>>>
>>>  From what you described here, I think we share a similar goal and have
>>> somewhat similar concerns (thanks, btw, it wasn't obvious to me before),
>>> we just disagree on the trade-offs and ideal solution :)
>>>
>>> I agree that we need to sanity check the drivers, and I don't want to go
>>> back to the situation we had before where drivers could just ignore
>>> infoframes and take the easy way out.
>>>
>>> It should be hard, and easy to catch during review.
>>>
>>> I don't think bitflag are a solution because, to me, it kind of fails
>>> both.
>>>
>>> What if, just like the debugfs discussion, we split write_infoframe into
>>> write_avi_infoframe (mandatory), write_spd_infoframe (optional),
>>> write_audio_infoframe (checked by drm_connector_hdmi_audio_init?) and
>>> write_hdr_infoframe (checked in drmm_connector_hdmi_init if max_bpc > 8)
>>>
>>> How does that sound?
>>
>> I'd say, I really like the single function to be called for writing the
>> infoframes. It makes it much harder for drivers to misbehave or to skip
>> something.
> 
>  From a driver PoV, I believe we should still have that single function
> indeed. It would be drm_atomic_helper_connector_hdmi_update_infoframes's
> job to fan out and call the multiple callbacks, not the drivers.

I like this idea, however it stops at the drm_bridge_connector 
abstraction. The only way to handle this I can foresee is to make 
individual bridges provide struct drm_connector_hdmi_funcs 
implementation (which I'm fine with) and store void *data or struct 
drm_bridge *hdmi_bridge somewhere inside struct drm_connector_hdmi in 
order to let bridge drivers find their data.

-- 
With best wishes
Dmitry