Commit 2914709c9141 for kernel

commit 2914709c914101eb704e01bed2351070d4161ccf
Author: Suraj Kandpal <suraj.kandpal@intel.com>
Date:   Sun May 17 08:17:09 2026 +0530

    Revert "drm/i915/backlight: Remove try_vesa_interface"

    This reverts commit 40d2f5820951dee818d05c14677277048bd85f9f.

    Removing the try_vesa_interface gate caused a backlight regression on
    panels whose VBT correctly reports INTEL_BACKLIGHT_DISPLAY_DDI and whose
    PWM path is the actual backlight control, but whose DPCD optimistically
    advertises DP_EDP_BACKLIGHT_AUX_ENABLE_CAP / _BRIGHTNESS_AUX_SET_CAP.
    After the commit such panels silently bind to the VESA AUX backlight
    funcs; AUX writes complete but the panel ignores them, leaving
    brightness stuck (no-op backlight). Observed on at least KBL and TGL
    eDP setups.

    Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
    Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
    Link: https://patch.msgid.link/20260517024709.1016121-1-suraj.kandpal@intel.com
    (cherry picked from commit f30fddb4402313aa5301a74d721638d343395269)
    Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>

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 a8d56ebf06a2..7a6c07f6aaeb 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -691,10 +691,9 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct drm_device *dev = connector->base.dev;
 	struct intel_panel *panel = &connector->panel;
-	bool try_intel_interface = false;
+	bool try_intel_interface = false, try_vesa_interface = false;

-	/*
-	 * Check the VBT and user's module parameters to figure out which
+	/* Check the VBT and user's module parameters to figure out which
 	 * interfaces to probe
 	 */
 	switch (display->params.enable_dpcd_backlight) {
@@ -703,6 +702,7 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 	case INTEL_DP_AUX_BACKLIGHT_AUTO:
 		switch (panel->vbt.backlight.type) {
 		case INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE:
+			try_vesa_interface = true;
 			break;
 		case INTEL_BACKLIGHT_DISPLAY_DDI:
 			try_intel_interface = true;
@@ -715,12 +715,20 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 		if (panel->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)
 			try_intel_interface = true;

+		try_vesa_interface = true;
+		break;
+	case INTEL_DP_AUX_BACKLIGHT_FORCE_VESA:
+		try_vesa_interface = true;
 		break;
 	case INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL:
 		try_intel_interface = true;
 		break;
 	}

+	/* For eDP 1.5 and above we are supposed to use VESA interface for brightness control */
+	if (intel_dp->edp_dpcd[0] >= DP_EDP_15)
+		try_vesa_interface = true;
+
 	/*
 	 * Since Intel has their own backlight control interface, the majority of machines out there
 	 * using DPCD backlight controls with Intel GPUs will be using this interface as opposed to
@@ -733,9 +741,6 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 	 * panel with Intel's OUI - which is also required for us to be able to detect Intel's
 	 * backlight interface at all. This means that the only sensible way for us to detect both
 	 * interfaces is to probe for Intel's first, and VESA's second.
-	 *
-	 * Also there is a chance some VBTs may advertise false Intel backlight support even if the
-	 * TCON DPCD says otherwise. This means we keep VESA interface as fallback in that case.
 	 */
 	if (try_intel_interface && intel_dp->edp_dpcd[0] <= DP_EDP_14b &&
 	    intel_dp_aux_supports_hdr_backlight(connector)) {
@@ -745,7 +750,7 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 		return 0;
 	}

-	if (intel_dp_aux_supports_vesa_backlight(connector)) {
+	if (try_vesa_interface && intel_dp_aux_supports_vesa_backlight(connector)) {
 		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using VESA eDP backlight controls\n",
 			    connector->base.base.id, connector->base.name);
 		panel->backlight.funcs = &intel_dp_vesa_bl_funcs;