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

[Lyude Paul]

On Wed, 2022-04-13 at 08:31 +0000, Hogander, Jouni wrote:
> 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?

Yes, probably - I think just making it so that i915.enable_dpcd_backlight=3
enables the HDR backlight regardless of the results of the EDID check would
probably be a good idea.

> 
> 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
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat