drm/i915: Check EDID for HDR static metadata when choosing blc

drm/i915: Check EDID for HDR static metadata when choosing blc

commit e2c69aafc9ffd97b382ce6582238525a870d45a3 upstream.

We have now seen panel (XMG Core 15 e21 laptop) advertizing 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
Intel proprietary eDP backlight control is used only if that exists.
Missing HDR static metadata is ignored if user specifically asks for
Intel proprietary eDP backlight control via enable_dpcd_backlight
parameter.

v2 :
- Ignore missing HDR static metadata if Intel proprietary eDP
  backlight control is forced via i915.enable_dpcd_backlight
- Printout info message if panel is missing HDR static metadata and
  support for Intel proprietary eDP backlight control is detected

Fixes: 83044126412f ("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@redhat.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Filippo Falezza <filippo.falezza@outlook.it>
Cc: stable@vger.kernel.org
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220413082826.120634-1-jouni.hogander@intel.com
Reviewed-by: Lyude Paul <lyude@redhat.com>
(cherry picked from commit 7be5eb2a2b1eb3d16fd2058ce0a1f4210851918d)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>