drm/i915/psr: Read Intel DPCD workaround register

Read Intel DPCD workaround register and store it into
intel_connector->dp.psr_caps. psr_caps was chosen as currently it contains
only PSR workaround for PSR2 SDP on prior scanline implementation.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patch.msgid.link/20260515095756.2799483-3-jouni.hogander@intel.com
(cherry picked from commit c48ff24)
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>

Author: hogander

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -584,6 +584,7 @@ struct intel_connector {
 
 		struct {
 			u8 dpcd[EDP_PSR_RECEIVER_CAP_SIZE];
+			u8 intel_wa_dpcd;
 
 			bool support;
 			bool su_support;

drivers/gpu/drm/i915/display/intel_psr.c

@@ -43,6 +43,7 @@
 #include "intel_display_wa.h"
 #include "intel_dmc.h"
 #include "intel_dp.h"
+#include "intel_dpcd.h"
 #include "intel_dp_aux.h"
 #include "intel_dsb.h"
 #include "intel_frontbuffer.h"
@@ -716,8 +717,14 @@ static void _psr_init_dpcd(struct intel_dp *intel_dp, struct intel_connector *co
 			    connector->dp.psr_caps.su_support ? "" : "not ");
 	}
 
-	if (connector->dp.psr_caps.su_support)
+	if (connector->dp.psr_caps.su_support) {
+		ret = drm_dp_dpcd_read_byte(&intel_dp->aux,
+					    INTEL_DPCD_INTEL_WA_REGISTER_CAPS,
+					    &connector->dp.psr_caps.intel_wa_dpcd);
+		if (ret < 0)
+			return;
 		_psr_compute_su_granularity(intel_dp, connector);
+	}
 }
 
 void intel_psr_init_dpcd(struct intel_dp *intel_dp, struct intel_connector *connector)