drm/i915/psr: enable ALPM for psr2

As per edp1.4 spec , alpm is required for psr2 operation as it's
used for all psr2  main link power down management and alpm enable
bit must be set for psr2 operation.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: vathsala nagaraju <vathsala.nagaraju@intel.com>
Signed-off-by: Patil Deepti <deepti.patil@intel.com>
Reviewed-by: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1483356663-32668-6-git-send-email-vathsala.nagaraju@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1156,6 +1156,7 @@ struct i915_psr {
 	bool link_standby;
 	bool y_cord_support;
 	bool colorimetry_support;
+	bool alpm;
 };
 
 enum intel_pch {

drivers/gpu/drm/i915/intel_dp.c

@@ -3060,6 +3060,14 @@ static bool intel_dp_get_colorimetry_status(struct intel_dp *intel_dp)
 	return dprx & DP_VSC_SDP_EXT_FOR_COLORIMETRY_SUPPORTED;
 }
 
+bool intel_dp_get_alpm_status(struct intel_dp *intel_dp)
+{
+	uint8_t alpm_caps = 0;
+
+	drm_dp_dpcd_readb(&intel_dp->aux, DP_RECEIVER_ALPM_CAP, &alpm_caps);
+	return alpm_caps & DP_ALPM_CAP;
+}
+
 /* These are source-specific values. */
 uint8_t
 intel_dp_voltage_max(struct intel_dp *intel_dp)
@@ -3644,6 +3652,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 				intel_dp_get_y_cord_status(intel_dp);
 			dev_priv->psr.colorimetry_support =
 				intel_dp_get_colorimetry_status(intel_dp);
+			dev_priv->psr.alpm =
+				intel_dp_get_alpm_status(intel_dp);
 		}
 
 	}

drivers/gpu/drm/i915/intel_psr.c

@@ -209,7 +209,11 @@ static void hsw_psr_enable_sink(struct intel_dp *intel_dp)
 		drm_dp_dpcd_writeb(&intel_dp->aux,
 				DP_SINK_DEVICE_AUX_FRAME_SYNC_CONF,
 				DP_AUX_FRAME_SYNC_ENABLE);
-
+	/* Enable ALPM at sink for psr2 */
+	if (dev_priv->psr.psr2_support && dev_priv->psr.alpm)
+		drm_dp_dpcd_writeb(&intel_dp->aux,
+				DP_RECEIVER_ALPM_CONFIG,
+				DP_ALPM_ENABLE);
 	if (dev_priv->psr.link_standby)
 		drm_dp_dpcd_writeb(&intel_dp->aux, DP_PSR_EN_CFG,
 				   DP_PSR_ENABLE | DP_PSR_MAIN_LINK_ACTIVE);