linux-kernel - Re: [PATCH v3 1/2] drm/bridge-connector: Prioritize supported_formats over ycbcr_420

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Message-ID: <7ct4feznensmvubaflaorqlw7uiuafwo5da5etsivogccrwdeh@r6jsztj4dsnh>
Date: Fri, 20 Dec 2024 03:05:53 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
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 v3 1/2] drm/bridge-connector: Prioritize
 supported_formats over ycbcr_420_allowed

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@...labora.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.

> 
> Thanks,
> Cristian

-- 
With best wishes
Dmitry