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 a8d56ebf06a2fd2271c370ca0b91fb16443e36df..7a6c07f6aaeb4b33d212d76d9915f415ea860327 100644 (file)
--- 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;