[SRU][R][PATCH v2 04/12] drm/i915/backlight: Remove try_vesa_interface

[Werner Sembach]

From: Suraj Kandpal <suraj.kandpal at intel.com>

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 at intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
Link: https://patch.msgid.link/20260224031322.2568874-1-suraj.kandpal@intel.com
Signed-off-by: Werner Sembach <wse at tuxedocomputers.com>
(cherry picked from commit 40d2f5820951dee818d05c14677277048bd85f9f)
Signed-off-by: Werner Sembach <wse at tuxedocomputers.com>
---
 .../drm/i915/display/intel_dp_aux_backlight.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

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 eb05ef4bd9f6c..517e32d7702d4 100644
--- 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;
-- 
2.43.0