drm/i915/psr: Timestamps for PSR entry and exit interrupts.

Timestamps are useful for IGT tests that trigger PSR exit and/or wait for
PSR entry.

v2: Removed seqlock (Ville)
    Removed erroneous warning in irq loop (Chris)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Jose Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180403212420.25007-4-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2686,6 +2686,13 @@ static int i915_edp_psr_status(struct seq_file *m, void *data)
 	}
 	mutex_unlock(&dev_priv->psr.lock);
 
+	if (READ_ONCE(dev_priv->psr.debug)) {
+		seq_printf(m, "Last attempted entry at: %lld\n",
+			   dev_priv->psr.last_entry_attempt);
+		seq_printf(m, "Last exit at: %lld\n",
+			   dev_priv->psr.last_exit);
+	}
+
 	intel_runtime_pm_put(dev_priv);
 	return 0;
 }

drivers/gpu/drm/i915/i915_drv.h

@@ -611,6 +611,8 @@ struct i915_psr {
 	bool psr2_enabled;
 	u8 sink_sync_latency;
 	bool debug;
+	ktime_t last_entry_attempt;
+	ktime_t last_exit;
 
 	void (*enable_source)(struct intel_dp *,
 			      const struct intel_crtc_state *);

drivers/gpu/drm/i915/intel_psr.c

@@ -129,6 +129,7 @@ void intel_psr_irq_handler(struct drm_i915_private *dev_priv, u32 psr_iir)
 {
 	u32 transcoders = BIT(TRANSCODER_EDP);
 	enum transcoder cpu_transcoder;
+	ktime_t time_ns =  ktime_get();
 
 	if (INTEL_GEN(dev_priv) >= 8)
 		transcoders |= BIT(TRANSCODER_A) |
@@ -141,14 +142,18 @@ void intel_psr_irq_handler(struct drm_i915_private *dev_priv, u32 psr_iir)
 			DRM_DEBUG_KMS("[transcoder %s] PSR aux error\n",
 				      transcoder_name(cpu_transcoder));
 
-		if (psr_iir & EDP_PSR_PRE_ENTRY(cpu_transcoder))
+		if (psr_iir & EDP_PSR_PRE_ENTRY(cpu_transcoder)) {
+			dev_priv->psr.last_entry_attempt = time_ns;
 			DRM_DEBUG_KMS("[transcoder %s] PSR entry attempt in 2 vblanks\n",
 				      transcoder_name(cpu_transcoder));
+		}
 
-		if (psr_iir & EDP_PSR_POST_EXIT(cpu_transcoder))
+		if (psr_iir & EDP_PSR_POST_EXIT(cpu_transcoder)) {
+			dev_priv->psr.last_exit = time_ns;
 			DRM_DEBUG_KMS("[transcoder %s] PSR exit completed\n",
 				      transcoder_name(cpu_transcoder));
 		}
+	}
 }
 
 static bool intel_dp_get_y_coord_required(struct intel_dp *intel_dp)