[PATCH 1/4] drm/i915: Check EDID before dpcd for possible HDR aux bl support

[Jouni Högander]

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;
+
 	intel_dp_wait_source_oui(intel_dp);
 
 	ret = drm_dp_dpcd_read(aux, INTEL_EDP_HDR_TCON_CAP0, tcon_cap, sizeof(tcon_cap));
-- 
2.25.1