[SRU][P][PATCH 3/8] drm/i915/backlight: Use proper interface based on eDP version

[En-Wei Wu]

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

BugLink: https://bugs.launchpad.net/bugs/2097818

eDP is supposed to use VESA interface when using revision 1.5 and above,
use Intel interface for backlight control otherwise. Add check to
use correct interface.

Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
Tested-by: Ben Kao <ben.kao at intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206063253.2827017-4-suraj.kandpal@intel.com
(cherry picked from commit 9535c6a4c61cc0da28b9c9986aad200f1e1019e4 linux-next)
Signed-off-by: En-Wei Wu <en-wei.wu at canonical.com>
---
 drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

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 c846ef4acf5b..09e82f24d030 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -604,6 +604,7 @@ static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 {
 	struct intel_display *display = to_intel_display(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;
@@ -640,6 +641,10 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 		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
@@ -653,7 +658,8 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 	 * 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.
 	 */
-	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) {
+	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector) &&
+	    intel_dp->edp_dpcd[0] <= DP_EDP_14b) {
 		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using Intel proprietary eDP backlight controls\n",
 			    connector->base.base.id, connector->base.name);
 		panel->backlight.funcs = &intel_dp_hdr_bl_funcs;
-- 
2.43.0