drm/i915/psr: Chase psr.enabled only under the psr.lock

Inside the psr work function, we want to wait for PSR to idle first and
wish to do so without blocking the normal modeset path, so we do so
without holding the PSR lock. However, we first have to find which pipe
PSR was enabled on, which requires chasing into the PSR struct and
requires locking to prevent intel_psr_disable() from concurrently
setting our pointer to NULL.

Fixes: 995d3047 ("drm/i915: VLV/CHV PSR Software timer mode")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Durgadoss R <durgadoss.r@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v4.0+
Reviewed-by: Jose Roberto de Souza <jose.souza@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405114915.29609-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_psr.c

@@ -775,53 +775,59 @@ void intel_psr_disable(struct intel_dp *intel_dp,
 	cancel_delayed_work_sync(&dev_priv->psr.work);
 }
 
-static void intel_psr_work(struct work_struct *work)
+static bool psr_wait_for_idle(struct drm_i915_private *dev_priv)
 {
-	struct drm_i915_private *dev_priv =
-		container_of(work, typeof(*dev_priv), psr.work.work);
-	struct intel_dp *intel_dp = dev_priv->psr.enabled;
-	struct drm_crtc *crtc = dp_to_dig_port(intel_dp)->base.base.crtc;
-	enum pipe pipe = to_intel_crtc(crtc)->pipe;
+	struct intel_dp *intel_dp;
+	i915_reg_t reg;
+	u32 mask;
+	int err;
+
+	intel_dp = dev_priv->psr.enabled;
+	if (!intel_dp)
+		return false;
 
-	/* We have to make sure PSR is ready for re-enable
-	 * otherwise it keeps disabled until next full enable/disable cycle.
-	 * PSR might take some time to get fully disabled
-	 * and be ready for re-enable.
-	 */
 	if (HAS_DDI(dev_priv)) {
 		if (dev_priv->psr.psr2_enabled) {
-			if (intel_wait_for_register(dev_priv,
-						    EDP_PSR2_STATUS,
-						    EDP_PSR2_STATUS_STATE_MASK,
-						    0,
-						    50)) {
-				DRM_ERROR("Timed out waiting for PSR2 Idle for re-enable\n");
-				return;
-			}
+			reg = EDP_PSR2_STATUS;
+			mask = EDP_PSR2_STATUS_STATE_MASK;
 		} else {
-			if (intel_wait_for_register(dev_priv,
-						    EDP_PSR_STATUS,
-						    EDP_PSR_STATUS_STATE_MASK,
-						    0,
-						    50)) {
-				DRM_ERROR("Timed out waiting for PSR Idle for re-enable\n");
-				return;
-			}
+			reg = EDP_PSR_STATUS;
+			mask = EDP_PSR_STATUS_STATE_MASK;
 		}
 	} else {
-		if (intel_wait_for_register(dev_priv,
-					    VLV_PSRSTAT(pipe),
-					    VLV_EDP_PSR_IN_TRANS,
-					    0,
-					    1)) {
-			DRM_ERROR("Timed out waiting for PSR Idle for re-enable\n");
-			return;
-		}
+		struct drm_crtc *crtc =
+			dp_to_dig_port(intel_dp)->base.base.crtc;
+		enum pipe pipe = to_intel_crtc(crtc)->pipe;
+
+		reg = VLV_PSRSTAT(pipe);
+		mask = VLV_EDP_PSR_IN_TRANS;
 	}
+
+	mutex_unlock(&dev_priv->psr.lock);
+
+	err = intel_wait_for_register(dev_priv, reg, mask, 0, 50);
+	if (err)
+		DRM_ERROR("Timed out waiting for PSR Idle for re-enable\n");
+
+	/* After the unlocked wait, verify that PSR is still wanted! */
 	mutex_lock(&dev_priv->psr.lock);
-	intel_dp = dev_priv->psr.enabled;
+	return err == 0 && dev_priv->psr.enabled;
+}
 
-	if (!intel_dp)
+static void intel_psr_work(struct work_struct *work)
+{
+	struct drm_i915_private *dev_priv =
+		container_of(work, typeof(*dev_priv), psr.work.work);
+
+	mutex_lock(&dev_priv->psr.lock);
+
+	/*
+	 * We have to make sure PSR is ready for re-enable
+	 * otherwise it keeps disabled until next full enable/disable cycle.
+	 * PSR might take some time to get fully disabled
+	 * and be ready for re-enable.
+	 */
+	if (!psr_wait_for_idle(dev_priv))
 		goto unlock;
 
 	/*
@@ -832,7 +838,7 @@ static void intel_psr_work(struct work_struct *work)
 	if (dev_priv->psr.busy_frontbuffer_bits)
 		goto unlock;
 
-	intel_psr_activate(intel_dp);
+	intel_psr_activate(dev_priv->psr.enabled);
 unlock:
 	mutex_unlock(&dev_priv->psr.lock);
 }