Re: [PATCH v2 4/7] drm/connector: hdmi: Use YUV420 output format as an RGB fallback

Dmitry Baryshkov
2025-03-11T19:46:44Z

On Tue, Mar 11, 2025 at 04:55:17PM +0100, Maxime Ripard wrote:
> Hi,
>
> I think the first thing we need to address is that we will need to
> differentiate between HDMI 1.4 devices and HDMI 2.0.
>
> It applies to YUV420, which is HDMI 2.0-only, and I guess your patches
> are good enough if you consider YUV420 support only, but scrambler setup
> for example is a thing we want to support in that infrastructure
> eventually, and is conditioned on HDMI 2.0 as well.
>
> On Tue, Mar 11, 2025 at 12:57:36PM +0200, Cristian Ciocaltea wrote:
> > Try to make use of YUV420 when computing the best output format and
> > RGB cannot be supported for any of the available color depths.
> >
> > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> > ---
> > drivers/gpu/drm/display/drm_hdmi_state_helper.c | 69 +++++++++++++------------
> > 1 file changed, 35 insertions(+), 34 deletions(-)
> >

[...]

> > return -EINVAL;
> > }
> >
> > +static int
> > +hdmi_compute_config(const struct drm_connector *connector,
> > + struct drm_connector_state *conn_state,
> > + const struct drm_display_mode *mode)
> > +{
> > + unsigned int max_bpc = clamp_t(unsigned int,
> > + conn_state->max_bpc,
> > + 8, connector->max_bpc);
> > + int ret;
> > +
> > + ret = hdmi_try_format(connector, conn_state, mode, max_bpc,
> > + HDMI_COLORSPACE_RGB);
> > + if (!ret)
> > + return 0;
> > +
> > + if (connector->ycbcr_420_allowed)
> > + ret = hdmi_try_format(connector, conn_state, mode, max_bpc,
> > + HDMI_COLORSPACE_YUV420);
>
> I think that's conditioned on a few more things:
> - That the driver supports HDMI 2.0

Isn't that included into connector->ycbcr_420_allowed? I'd expect that
HDMI 1.4-only drivers don't set that flag.

> - That the display is an HDMI output
> - That the mode is allowed YUV420 by the sink EDIDs
>
> > + else
> > + drm_dbg_kms(connector->dev,
> > + "%s output format not allowed for connector\n",
> > + drm_hdmi_connector_get_output_format_name(HDMI_COLORSPACE_YUV420));
>
> And I think we should keep the catch-all failure message we had.
>
> Maxime

--
With best wishes
Dmitry