drm/i915/dp: Cache the DP/eDP DSC DPCD register set on Hotplug/eDP Init

DSC is supported on eDP starting GEN 10 display (on GLK) and on DP starting
GEN 11.
This patch implements the discovery phase of DSC. On hotplug,
source reads the DSC DPCD register set (0x00060 - 0x0006F) to
read the decompression capabilities of the sink device.
This entire block of registers is cached in intel_dp so that
capability information can be used during DSC configuration
phase during compute_config phase of the modeset.
For eDP, this caching happens during the eDP initialization.
This caching is done only for eDP and DP rev >= 1.4

v5:
* Fix the block comment (Gaurav)
* Fix the commit message DSC DPCD addresses (Gaurav)
* Use DRM_ERROR for dpcd_read fail (Gaurav,Anusha)
v4:
* Cache these only for Gen >= 11
v3:
* Remove the dsc_sink_support field in intel_dp (Jani N)
v2:
* Clear the cached registers on hotplug always (Jani N)
* Combine the eDP and DP caching in same function (Jani N)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Gaurav K Singh <gaurav.k.singh@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Gaurav K Singh <gaurav.k.singh@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181031001923.31442-3-manasi.d.navare@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -3956,6 +3956,29 @@ intel_dp_read_dpcd(struct intel_dp *intel_dp)
 	return intel_dp->dpcd[DP_DPCD_REV] != 0;
 }
 
+static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
+{
+	/*
+	 * Clear the cached register set to avoid using stale values
+	 * for the sinks that do not support DSC.
+	 */
+	memset(intel_dp->dsc_dpcd, 0, sizeof(intel_dp->dsc_dpcd));
+
+	/* Cache the DSC DPCD if eDP or DP rev >= 1.4 */
+	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x14 ||
+	    intel_dp->edp_dpcd[0] >= DP_EDP_14) {
+		if (drm_dp_dpcd_read(&intel_dp->aux, DP_DSC_SUPPORT,
+				     intel_dp->dsc_dpcd,
+				     sizeof(intel_dp->dsc_dpcd)) < 0)
+			DRM_ERROR("Failed to read DPCD register 0x%x\n",
+				  DP_DSC_SUPPORT);
+
+		DRM_DEBUG_KMS("DSC DPCD: %*ph\n",
+			      (int)sizeof(intel_dp->dsc_dpcd),
+			      intel_dp->dsc_dpcd);
+	}
+}
+
 static bool
 intel_edp_init_dpcd(struct intel_dp *intel_dp)
 {
@@ -4032,6 +4055,10 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 
 	intel_dp_set_common_rates(intel_dp);
 
+	/* Read the eDP DSC DPCD registers */
+	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
+		intel_dp_get_dsc_sink_cap(intel_dp);
+
 	return true;
 }
 
@@ -5126,6 +5153,7 @@ intel_dp_detect(struct drm_connector *connector,
 
 	if (status == connector_status_disconnected) {
 		memset(&intel_dp->compliance, 0, sizeof(intel_dp->compliance));
+		memset(intel_dp->dsc_dpcd, 0, sizeof(intel_dp->dsc_dpcd));
 
 		if (intel_dp->is_mst) {
 			DRM_DEBUG_KMS("MST device may have disappeared %d vs %d\n",
@@ -5151,6 +5179,10 @@ intel_dp_detect(struct drm_connector *connector,
 
 	intel_dp_print_rates(intel_dp);
 
+	/* Read DP Sink DSC Cap DPCD regs for DP v1.4 */
+	if (INTEL_GEN(dev_priv) >= 11)
+		intel_dp_get_dsc_sink_cap(intel_dp);
+
 	drm_dp_read_desc(&intel_dp->aux, &intel_dp->desc,
 			 drm_dp_is_branch(intel_dp->dpcd));
 

drivers/gpu/drm/i915/intel_drv.h

@@ -1114,6 +1114,7 @@ struct intel_dp {
 	uint8_t psr_dpcd[EDP_PSR_RECEIVER_CAP_SIZE];
 	uint8_t downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
 	uint8_t edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
+	u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE];
 	/* source rates */
 	int num_source_rates;
 	const int *source_rates;