linux-kernel - Re: [PATCH v2] drm/bridge-connector: Prioritize supported_formats over ycbcr_420

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Message-ID: <d1fe66a7-c495-429d-9908-6f4076a994da@collabora.com>
Date: Tue, 17 Dec 2024 01:17:48 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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>,
 kernel@...labora.com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge-connector: Prioritize supported_formats
 over ycbcr_420_allowed

Hi Dmitry,

On 12/10/24 3:12 AM, Dmitry Baryshkov wrote:
> On Fri, Dec 06, 2024 at 10:00:46PM +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.
> 
> I think this should be handled in a different way: during HDMI connector
> init verify that HDMI_COLORSPACE_YUV420 matches the
> drm_connector->ycbcr_420_allowed value and rejects incompatible
> connectors.

I added a 2nd patch in v3 [1] to perform this verification on HDMI
connector init, but I think we still need a proper handling of the
inconsistency at bridge[-connector] level. I simplified a bit the initial
approach, hopefully that would bring us closer to an acceptable solution.

Thanks,
Cristian

[1] https://lore.kernel.org/lkml/20241217-bridge-conn-fmt-prio-v3-0-3ecb3c8fc06f@collabora.com/