drm/i915/psr: Get pipe id following atomic guidelines

As stated in struct drm_encoder, crtc field should only be used
by non-atomic drivers.

So here caching the pipe id in intel_psr_enable() what is way more
simple and efficient than at every call to
intel_psr_flush()/invalidate() get the
drm.mode_config.connection_mutex lock to safely be able to get the
pipe id by reading drm_connector_state.crtc.

This should fix the null pointer dereference crash below as the
previous way to get the pipe id was prone to race conditions.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105959
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128072838.22773-1-jose.souza@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -495,6 +495,7 @@ struct i915_psr {
 	bool sink_support;
 	bool prepared, enabled;
 	struct intel_dp *dp;
+	enum pipe pipe;
 	bool active;
 	struct work_struct work;
 	unsigned busy_frontbuffer_bits;

drivers/gpu/drm/i915/intel_psr.c

@@ -719,6 +719,7 @@ void intel_psr_enable(struct intel_dp *intel_dp,
 	dev_priv->psr.psr2_enabled = intel_psr2_enabled(dev_priv, crtc_state);
 	dev_priv->psr.busy_frontbuffer_bits = 0;
 	dev_priv->psr.prepared = true;
+	dev_priv->psr.pipe = to_intel_crtc(crtc_state->base.crtc)->pipe;
 
 	if (psr_global_enabled(dev_priv->psr.debug))
 		intel_psr_enable_locked(dev_priv, crtc_state);
@@ -1026,9 +1027,6 @@ static void intel_psr_work(struct work_struct *work)
 void intel_psr_invalidate(struct drm_i915_private *dev_priv,
 			  unsigned frontbuffer_bits, enum fb_op_origin origin)
 {
-	struct drm_crtc *crtc;
-	enum pipe pipe;
-
 	if (!CAN_PSR(dev_priv))
 		return;
 
@@ -1041,10 +1039,7 @@ void intel_psr_invalidate(struct drm_i915_private *dev_priv,
 		return;
 	}
 
-	crtc = dp_to_dig_port(dev_priv->psr.dp)->base.base.crtc;
-	pipe = to_intel_crtc(crtc)->pipe;
-
-	frontbuffer_bits &= INTEL_FRONTBUFFER_ALL_MASK(pipe);
+	frontbuffer_bits &= INTEL_FRONTBUFFER_ALL_MASK(dev_priv->psr.pipe);
 	dev_priv->psr.busy_frontbuffer_bits |= frontbuffer_bits;
 
 	if (frontbuffer_bits)
@@ -1069,9 +1064,6 @@ void intel_psr_invalidate(struct drm_i915_private *dev_priv,
 void intel_psr_flush(struct drm_i915_private *dev_priv,
 		     unsigned frontbuffer_bits, enum fb_op_origin origin)
 {
-	struct drm_crtc *crtc;
-	enum pipe pipe;
-
 	if (!CAN_PSR(dev_priv))
 		return;
 
@@ -1084,10 +1076,7 @@ void intel_psr_flush(struct drm_i915_private *dev_priv,
 		return;
 	}
 
-	crtc = dp_to_dig_port(dev_priv->psr.dp)->base.base.crtc;
-	pipe = to_intel_crtc(crtc)->pipe;
-
-	frontbuffer_bits &= INTEL_FRONTBUFFER_ALL_MASK(pipe);
+	frontbuffer_bits &= INTEL_FRONTBUFFER_ALL_MASK(dev_priv->psr.pipe);
 	dev_priv->psr.busy_frontbuffer_bits &= ~frontbuffer_bits;
 
 	/* By definition flush = invalidate + flush */
@@ -1101,7 +1090,7 @@ void intel_psr_flush(struct drm_i915_private *dev_priv,
 		 * but it makes more sense write to the current active
 		 * pipe.
 		 */
-		I915_WRITE(CURSURFLIVE(pipe), 0);
+		I915_WRITE(CURSURFLIVE(dev_priv->psr.pipe), 0);
 	}
 
 	if (!dev_priv->psr.active && !dev_priv->psr.busy_frontbuffer_bits)