Re: [PATCH v3 1/2] drm/bridge-connector: Prioritize supported_formats over ycbcr_420_allowed

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

On 12/17/24 1:27 AM, Dmitry Baryshkov wrote:
> On Tue, Dec 17, 2024 at 12:54:07AM +0200, Cristian Ciocaltea wrote:
>> Bridges having the DRM_BRIDGE_OP_HDMI flag set in drm_bridge->ops are
>> supposed to rely on drm_bridge->supported_formats bitmask to advertise
>> the supported colorspaces, including HDMI_COLORSPACE_YUV420.  Therefore,
>> the newly introduced drm_bridge->ycbcr_420_allowed flag becomes
>> redundant in this particular context.
>>
>> Moreover, when drm_bridge_connector gets initialised, only
>> drm_bridge->ycbcr_420_allowed is considered in the process of adjusting
>> the equivalent property of the base drm_connector, which effectively
>> discards the formats advertised by the HDMI bridge.
>>
>> Handle the inconsistency by overwriting drm_bridge->ycbcr_420_allowed
>> for HDMI bridges according to drm_bridge->supported_formats, before
>> adding them to the global bridge list.
>>
>> Additionally, ensure the YUV420 related bit is removed from the bitmask
>> passed to drmm_connector_hdmi_init() when the final ycbcr_420_allowed
>> flag for the connector ends up not being set (i.e. the case of having at
>> least one non-HDMI bridge in the pipeline that didn't enable it).
>>
>> Fixes: 3ced1c687512 ("drm/display: bridge_connector: handle ycbcr_420_allowed")
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>> ---
>>  drivers/gpu/drm/display/drm_bridge_connector.c | 8 ++++++--
>>  drivers/gpu/drm/drm_bridge.c                   | 4 ++++
>>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> I think the second patch in the series is enough, it ensures that
> connector's state is consistent, no matter if the drm_bridge_connector
> is being used or a normal drm_connector.
> 
> Nevertheless, I'd leave the final decision to DRM maintainers.

This patch has 2 parts, maybe I should have put them into separate patches
as they kind of relate to distinct problems.

The 1st part makes sure that drm_bridge->ycbcr_420_allowed is automatically
set when HDMI_COLORSPACE_YUV420 is provided in drm_bridge->supported_formats, 
to avoid the need of requiring redundant information on HDMI bridges 
initialization.  This implicitly ensures the consistency needed to further 
allow relying on ->ycbcr_420_allowed internally.

While the 1st part could be dropped (assuming redundancy & consistency is
not really something we want/need to handle), the 2nd part I think is
mandatory, i.e. we must adjust supported_formats before calling
drmm_connector_hdmi_init() to ensure the presence of HDMI_COLORSPACE_YUV420
reflects the status of the computed connector->ycbcr_420_allowed, which
might end up being different than what the HDMI bridge advertised, i.e. the
case of having an HDMI bridge in the pipeline advertising YUV420 via 
supported_formats and a non-HDMI one that didn't enable ycbcr_420_allowed.

Thanks,
Cristian