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

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

On 12/20/24 3:05 AM, Dmitry Baryshkov wrote:
> On Tue, Dec 17, 2024 at 02:38:55AM +0200, Cristian Ciocaltea wrote:
>> 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.
> 
> Please split it into two patches. I don't have a strong opinion upon the
> first one (I'd change it to dev_warn() maybe), while the second one
> (removing HDMI_COLORSPACE_YUV420 if connector->ycbcr_420_allowed is
> false) is definitely a correct change.

Split done in v4:

https://lore.kernel.org/lkml/20241224-bridge-conn-fmt-prio-v4-2-a9ceb5671379@collabora.com/

Thanks,
Cristian