drm/msm/mdp4: cure for the cursor blues (v2)

The hw cursor is relatively adept at triggering underflows, which
manifest as a "blue flash" (since blue is configured as the underflow
color).  Juggle a few things around to tighten up the timing for setting
cursor registers in DONE irq.

And most importantly, don't ever disable the hw cursor.  Instead flip it
to a blank/empty cursor.  This seems far more reliable, as even simply
clearing the cursor-enable bit (with no other updates in previous/
following frames) can in some cases cause underflow.

v1: original
v2: add missing locking spotted by Micah

Cc: Micah Richert <richert@braincorporation.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/mdp/mdp4/mdp4_crtc.c

@@ -510,9 +510,8 @@ static void update_cursor(struct drm_crtc *crtc)
 					MDP4_DMA_CURSOR_BLEND_CONFIG_CURSOR_EN);
 		} else {
 			/* disable cursor: */
-			mdp4_write(mdp4_kms, REG_MDP4_DMA_CURSOR_BASE(dma), 0);
-			mdp4_write(mdp4_kms, REG_MDP4_DMA_CURSOR_BLEND_CONFIG(dma),
-					MDP4_DMA_CURSOR_BLEND_CONFIG_FORMAT(CURSOR_ARGB));
+			mdp4_write(mdp4_kms, REG_MDP4_DMA_CURSOR_BASE(dma),
+					mdp4_kms->blank_cursor_iova);
 		}
 
 		/* and drop the iova ref + obj rev when done scanning out: */
@@ -574,11 +573,9 @@ static int mdp4_crtc_cursor_set(struct drm_crtc *crtc,
 
 	if (old_bo) {
 		/* drop our previous reference: */
-		msm_gem_put_iova(old_bo, mdp4_kms->id);
-		drm_gem_object_unreference_unlocked(old_bo);
+		drm_flip_work_queue(&mdp4_crtc->unref_cursor_work, old_bo);
 	}
 
-	crtc_flush(crtc);
 	request_pending(crtc, PENDING_CURSOR);
 
 	return 0;

drivers/gpu/drm/msm/mdp/mdp4/mdp4_irq.c

@@ -70,12 +70,12 @@ irqreturn_t mdp4_irq(struct msm_kms *kms)
 
 	VERB("status=%08x", status);
 
+	mdp_dispatch_irqs(mdp_kms, status);
+
 	for (id = 0; id < priv->num_crtcs; id++)
 		if (status & mdp4_crtc_vblank(priv->crtcs[id]))
 			drm_handle_vblank(dev, id);
 
-	mdp_dispatch_irqs(mdp_kms, status);
-
 	return IRQ_HANDLED;
 }
 

drivers/gpu/drm/msm/mdp/mdp4/mdp4_kms.c

@@ -144,6 +144,10 @@ static void mdp4_preclose(struct msm_kms *kms, struct drm_file *file)
 static void mdp4_destroy(struct msm_kms *kms)
 {
 	struct mdp4_kms *mdp4_kms = to_mdp4_kms(to_mdp_kms(kms));
+	if (mdp4_kms->blank_cursor_iova)
+		msm_gem_put_iova(mdp4_kms->blank_cursor_bo, mdp4_kms->id);
+	if (mdp4_kms->blank_cursor_bo)
+		drm_gem_object_unreference(mdp4_kms->blank_cursor_bo);
 	kfree(mdp4_kms);
 }
 
@@ -372,6 +376,23 @@ struct msm_kms *mdp4_kms_init(struct drm_device *dev)
 		goto fail;
 	}
 
+	mutex_lock(&dev->struct_mutex);
+	mdp4_kms->blank_cursor_bo = msm_gem_new(dev, SZ_16K, MSM_BO_WC);
+	mutex_unlock(&dev->struct_mutex);
+	if (IS_ERR(mdp4_kms->blank_cursor_bo)) {
+		ret = PTR_ERR(mdp4_kms->blank_cursor_bo);
+		dev_err(dev->dev, "could not allocate blank-cursor bo: %d\n", ret);
+		mdp4_kms->blank_cursor_bo = NULL;
+		goto fail;
+	}
+
+	ret = msm_gem_get_iova(mdp4_kms->blank_cursor_bo, mdp4_kms->id,
+			&mdp4_kms->blank_cursor_iova);
+	if (ret) {
+		dev_err(dev->dev, "could not pin blank-cursor bo: %d\n", ret);
+		goto fail;
+	}
+
 	return kms;
 
 fail:

drivers/gpu/drm/msm/mdp/mdp4/mdp4_kms.h

@@ -44,6 +44,10 @@ struct mdp4_kms {
 	struct clk *lut_clk;
 
 	struct mdp_irq error_handler;
+
+	/* empty/blank cursor bo to use when cursor is "disabled" */
+	struct drm_gem_object *blank_cursor_bo;
+	uint32_t blank_cursor_iova;
 };
 #define to_mdp4_kms(x) container_of(x, struct mdp4_kms, base)
 

drivers/gpu/drm/msm/mdp/mdp5/mdp5_irq.c

@@ -71,11 +71,11 @@ static void mdp5_irq_mdp(struct mdp_kms *mdp_kms)
 
 	VERB("status=%08x", status);
 
+	mdp_dispatch_irqs(mdp_kms, status);
+
 	for (id = 0; id < priv->num_crtcs; id++)
 		if (status & mdp5_crtc_vblank(priv->crtcs[id]))
 			drm_handle_vblank(dev, id);
-
-	mdp_dispatch_irqs(mdp_kms, status);
 }
 
 irqreturn_t mdp5_irq(struct msm_kms *kms)