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

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: 4a8d7990 ("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.comReviewed-by: Lyude Paul <lyude@redhat.com>

drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c

@@ -97,6 +97,14 @@
 
 #define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_1                            0x359
 
+enum intel_dp_aux_backlight_modparam {
+	INTEL_DP_AUX_BACKLIGHT_AUTO = -1,
+	INTEL_DP_AUX_BACKLIGHT_OFF = 0,
+	INTEL_DP_AUX_BACKLIGHT_ON = 1,
+	INTEL_DP_AUX_BACKLIGHT_FORCE_VESA = 2,
+	INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL = 3,
+};
+
 /* Intel EDP backlight callbacks */
 static bool
 intel_dp_aux_supports_hdr_backlight(struct intel_connector *connector)
@@ -126,6 +134,24 @@ intel_dp_aux_supports_hdr_backlight(struct intel_connector *connector)
 		return false;
 	}
 
+	/*
+	 * 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 (i915->params.enable_dpcd_backlight != INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL &&
+	    !(connector->base.hdr_sink_metadata.hdmi_type1.metadata_type &
+	      BIT(HDMI_STATIC_METADATA_TYPE1))) {
+		drm_info(&i915->drm,
+			 "Panel is missing HDR static metadata. Possible support for Intel HDR backlight interface is not used. If your backlight controls don't work try booting with i915.enable_dpcd_backlight=%d. needs this, please file a _new_ bug report on drm/i915, see " FDO_BUG_URL " for details.\n",
+			 INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL);
+		return false;
+	}
+
 	panel->backlight.edp.intel.sdr_uses_aux =
 		tcon_cap[2] & INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP;
 
@@ -413,14 +439,6 @@ static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
 	.get = intel_dp_aux_vesa_get_backlight,
 };
 
-enum intel_dp_aux_backlight_modparam {
-	INTEL_DP_AUX_BACKLIGHT_AUTO = -1,
-	INTEL_DP_AUX_BACKLIGHT_OFF = 0,
-	INTEL_DP_AUX_BACKLIGHT_ON = 1,
-	INTEL_DP_AUX_BACKLIGHT_FORCE_VESA = 2,
-	INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL = 3,
-};
-
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 {
 	struct drm_device *dev = connector->base.dev;