drm/i915/psr: Set idle frame count based on sink synchronization latency

DPCD 2009h "Synchronization latency in sink" has bits that tell us the
maximum number of frames sink can take to resynchronize to source timing
when exiting PSR. More importantly, as per eDP 1.4b, this is the "Minimum
number of frames following PSR exit that the Source device needs to
wait for PSR entry."

We currently use this value only to setup the number frames to wait before
PSR2 selective update. But, based on the above description it makes more
sense to use this to configure idle frames for both PSR1 and and PSR2. This
will ensure we wait the required number of frames before
activation whether it is PSR1 or PSR2.

The minimum number of idle frames remains 6, while allowing sink
synchronization latency and VBT to increase this value.

This also solves the flip-flop between sink and source frames that I
noticed on my Thinkpad X260 during PSR exit. This specific panel has a
value of 8h, which according to the spec means the "Source device must
wait for more than eight active frames after PSR exit before initiating PSR
entry. (In this case, should be provided by the panel supplier.)" VBT
however has a value of 0.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jose Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525033047.7596-1-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/intel_psr.c

@@ -247,6 +247,8 @@ void intel_psr_init_dpcd(struct intel_dp *intel_dp)
 		return;
 	}
 	dev_priv->psr.sink_support = true;
+	dev_priv->psr.sink_sync_latency =
+		intel_dp_get_sink_sync_latency(intel_dp);
 
 	if (INTEL_GEN(dev_priv) >= 9 &&
 	    (intel_dp->psr_dpcd[0] == DP_PSR2_WITH_Y_COORD_IS_SUPPORTED)) {
@@ -272,8 +274,6 @@ void intel_psr_init_dpcd(struct intel_dp *intel_dp)
 		if (dev_priv->psr.sink_psr2_support) {
 			dev_priv->psr.colorimetry_support =
 				intel_dp_get_colorimetry_status(intel_dp);
-			dev_priv->psr.sink_sync_latency =
-				intel_dp_get_sink_sync_latency(intel_dp);
 		}
 	}
 }
@@ -370,21 +370,21 @@ static void hsw_activate_psr1(struct intel_dp *intel_dp)
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct drm_device *dev = dig_port->base.base.dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
+	u32 max_sleep_time = 0x1f;
+	u32 val = EDP_PSR_ENABLE;
 
-	uint32_t max_sleep_time = 0x1f;
-	/*
-	 * Let's respect VBT in case VBT asks a higher idle_frame value.
-	 * Let's use 6 as the minimum to cover all known cases including
-	 * the off-by-one issue that HW has in some cases. Also there are
-	 * cases where sink should be able to train
-	 * with the 5 or 6 idle patterns.
+	/* Let's use 6 as the minimum to cover all known cases including the
+	 * off-by-one issue that HW has in some cases.
 	 */
-	uint32_t idle_frames = max(6, dev_priv->vbt.psr.idle_frames);
-	uint32_t val = EDP_PSR_ENABLE;
+	int idle_frames = max(6, dev_priv->vbt.psr.idle_frames);
 
-	val |= max_sleep_time << EDP_PSR_MAX_SLEEP_TIME_SHIFT;
+	/* sink_sync_latency of 8 means source has to wait for more than 8
+	 * frames, we'll go with 9 frames for now
+	 */
+	idle_frames = max(idle_frames, dev_priv->psr.sink_sync_latency + 1);
 	val |= idle_frames << EDP_PSR_IDLE_FRAME_SHIFT;
 
+	val |= max_sleep_time << EDP_PSR_MAX_SLEEP_TIME_SHIFT;
 	if (IS_HASWELL(dev_priv))
 		val |= EDP_PSR_MIN_LINK_ENTRY_TIME_8_LINES;
 
@@ -424,15 +424,15 @@ static void hsw_activate_psr2(struct intel_dp *intel_dp)
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct drm_device *dev = dig_port->base.base.dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
-	/*
-	 * Let's respect VBT in case VBT asks a higher idle_frame value.
-	 * Let's use 6 as the minimum to cover all known cases including
-	 * the off-by-one issue that HW has in some cases. Also there are
-	 * cases where sink should be able to train
-	 * with the 5 or 6 idle patterns.
+	u32 val;
+
+	/* Let's use 6 as the minimum to cover all known cases including the
+	 * off-by-one issue that HW has in some cases.
 	 */
-	uint32_t idle_frames = max(6, dev_priv->vbt.psr.idle_frames);
-	u32 val = idle_frames << EDP_PSR2_IDLE_FRAME_SHIFT;
+	int idle_frames = max(6, dev_priv->vbt.psr.idle_frames);
+
+	idle_frames = max(idle_frames, dev_priv->psr.sink_sync_latency + 1);
+	val = idle_frames << EDP_PSR2_IDLE_FRAME_SHIFT;
 
 	/* FIXME: selective update is probably totally broken because it doesn't
 	 * mesh at all with our frontbuffer tracking. And the hw alone isn't