linux-kernel - Re: [PATCH 3/6] drm/bridge: display-connector: allow YCbCr 420 for HDMI and DP

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Message-ID: <CAA8EJprfpKqJBvrS_dLKy40LHOaL4XVSpmXMGP__z1jsOjZ7Ag@mail.gmail.com>
Date: Mon, 21 Oct 2024 12:06:46 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: neil.armstrong@...aro.org
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 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>, 
	Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 3/6] drm/bridge: display-connector: allow YCbCr 420 for
 HDMI and DP

On Mon, 21 Oct 2024 at 10:29, Neil Armstrong <neil.armstrong@...aro.org> wrote:
>
> On 18/10/2024 23:49, Dmitry Baryshkov wrote:
> > Allow YCbCr 420 output for HDMI and DisplayPort connectors. Other
> > bridges in the chain still might limit YCbCr 420 support on the
> > corresponding connector.
> >
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > ---
> >   drivers/gpu/drm/bridge/display-connector.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/display-connector.c b/drivers/gpu/drm/bridge/display-connector.c
> > index ab8e00baf3f1..aab9ce7be94c 100644
> > --- a/drivers/gpu/drm/bridge/display-connector.c
> > +++ b/drivers/gpu/drm/bridge/display-connector.c
> > @@ -270,6 +270,10 @@ static int display_connector_probe(struct platform_device *pdev)
> >       /* All the supported connector types support interlaced modes. */
> >       conn->bridge.interlace_allowed = true;
> >
> > +     if (type == DRM_MODE_CONNECTOR_HDMIA ||
> > +         type == DRM_MODE_CONNECTOR_DisplayPort)
> > +             conn->bridge.ycbcr_420_allowed = true;
> > +
> >       /* Get the optional connector label. */
> >       of_property_read_string(pdev->dev.of_node, "label", &label);
> >
> >
>
> I think we should make sure all HDMI bridges can filter out 420 before
> landing this, no ?

No, it's the other way around: if one of the bridges in a chain
doesn't set 420_allowed, then 420_allowed won't be set for the
connector, disallowing YCbCr 420 modes.
Before this patchset the bridge / platform drivers had to manually set
the flag on the created connector (see dw-hdmi + meson-encoder-hdmi or
msm/dp).

-- 
With best wishes
Dmitry