drm/i915/backlight: Remove try_vesa_interface

Some panels need VESA DPCD AUX backlight but VBT says otherwise.
This is why we try with Intel backlight interface over VESA backlight
interface. This causes a blankout on such panels without any fallback
mechanism.
Remove try_vesa_interface and use VESA AUX backlight interface as a
fallback mechanism.
While at in sneak in a small comment cleanup too.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/15679
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patch.msgid.link/20260224031322.2568874-1-suraj.kandpal@intel.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 eb05ef4bd9f6cc081d6bf88d71ff2a7c3740dc68..517e32d7702d46d6973da0b0869d9687890135e8 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -644,9 +644,10 @@ 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, try_vesa_interface = false;
+       bool try_intel_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) {
@@ -655,7 +656,6 @@ 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;
@@ -668,20 +668,12 @@ 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
@@ -694,6 +686,9 @@ 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_aux_supports_hdr_backlight(connector) &&
            intel_dp->edp_dpcd[0] <= DP_EDP_14b) {
@@ -703,7 +698,7 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
                return 0;
        }
 
-       if (try_vesa_interface && intel_dp_aux_supports_vesa_backlight(connector)) {
+       if (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;