[Intel-gfx] [PATCH] drm/i915: Check EDID before dpcd for possible HDR aux bl support

[Hogander, Jouni]

Hello Lyude,

See my respose below.

On Tue, 2022-04-12 at 13:50 -0400, Lyude Paul wrote:
> On Tue, 2022-04-12 at 08:25 +0300, Jouni Högander wrote:
> > We have now seen panel (XMG Core 15 e21 laptop) avertizing support
> > for Intel proprietary eDP backlight control via DPCD registers, but
> > actually working only with legacy pwm control.
> > 
> > This patch adds panel EDID check for possible HDR static metadata
> > and
> > does detection from DPCD registers only if this data block exists.
> > 
> > Fixes: 4a8d79901d5b ("drm/i915/dp: Enable Intel's HDR backlight
> > interface
> > (only SDR for now)")
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5284
> > Cc: Lyude Paul <lyude at redhat.com>
> > Cc: Mika Kahola <mika.kahola at intel.com>
> > Cc: Jani Nikula <jani.nikula at intel.com>
> > Tested-by: Filippo Falezza <filippo.falezza at outlook.it>
> > Signed-off-by: Jouni Högander <jouni.hogander at intel.com>
> > ---
> >  .../gpu/drm/i915/display/intel_dp_aux_backlight.c   | 13
> > +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > index 97cf3cac0105..f69e185b58c1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -108,6 +108,19 @@ intel_dp_aux_supports_hdr_backlight(struct
> > intel_connector *connector)
> >         int ret;
> >         u8 tcon_cap[4];
> >  
> > +       /*
> > +        * If we don't have HDR static metadata there is no way to
> > +        * runtime detect used range for nits based control. For
> > now
> > +        * do not use Intel proprietary eDP backlight control if we
> > +        * don't have this data in panel EDID. In case we find
> > panel
> > +        * which supports only nits based control, but doesn't
> > provide
> > +        * HDR static metadata we need to start maintaining table
> > of
> > +        * ranges for such panels.
> > +        */
> > +       if (!(connector-
> > >base.hdr_sink_metadata.hdmi_type1.metadata_type &
> > +             BIT(HDMI_STATIC_METADATA_TYPE1)))
> > +               return false;
> 
> The block used for this is actually for HDMI?? How bizarre…
> 
> Anyway yeah - patch looks good to me, but I think we should print a
> debugging
> message of some sort when we determine that there's no HDR backlight
> because
> of the EDID - along with printing instructions for how the user can
> override
> it if we've made the wrong choice along with reporting a bug. Also -
> we should
> have the

hmm, currently there is no override possibility
in intel_dp_aux_supports_hdr_backlight. Do you think I should add one?

I sent version 2. Didn't add your rb there as I wasn't sure if I
understood your comment correctly. Please check new version.

> Cc: stable at vger.kernel.org

tag from dim added here using `dim fixes $commit`.

With that fixed:

Reviewed-by: Lyude Paul <lyude at redhat.com>

+
        intel_dp_wait_source_oui(intel_dp);
 
        ret = drm_dp_dpcd_read(aux, INTEL_EDP_HDR_TCON_CAP0,
tcon_cap,
sizeof(tcon_cap));

BR,

Jouni Högander