drm/msm/atomic: Drop per-CRTC locks in reverse order

lockdep dislikes seeing locks unwound in a non-nested fashion.

Fixes: b3d91800d9 ("drm/msm: Fix race condition in msm driver with async layer updates")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>

drivers/gpu/drm/msm/msm_atomic.c

@@ -67,7 +67,7 @@ static void unlock_crtcs(struct msm_kms *kms, unsigned int crtc_mask)
 {
 	struct drm_crtc *crtc;
 
-	for_each_crtc_mask(kms->dev, crtc, crtc_mask)
+	for_each_crtc_mask_reverse(kms->dev, crtc, crtc_mask)
 		mutex_unlock(&kms->commit_lock[drm_crtc_index(crtc)]);
 }
 

drivers/gpu/drm/msm/msm_kms.h

@@ -196,4 +196,8 @@ int dpu_mdss_init(struct drm_device *dev);
 	drm_for_each_crtc(crtc, dev) \
 		for_each_if (drm_crtc_mask(crtc) & (crtc_mask))
 
+#define for_each_crtc_mask_reverse(dev, crtc, crtc_mask) \
+	drm_for_each_crtc_reverse(crtc, dev) \
+		for_each_if (drm_crtc_mask(crtc) & (crtc_mask))
+
 #endif /* __MSM_KMS_H__ */

include/drm/drm_crtc.h

@@ -1266,4 +1266,14 @@ static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,
 #define drm_for_each_crtc(crtc, dev) \
 	list_for_each_entry(crtc, &(dev)->mode_config.crtc_list, head)
 
+/**
+ * drm_for_each_crtc_reverse - iterate over all CRTCs in reverse order
+ * @crtc: a &struct drm_crtc as the loop cursor
+ * @dev: the &struct drm_device
+ *
+ * Iterate over all CRTCs of @dev.
+ */
+#define drm_for_each_crtc_reverse(crtc, dev) \
+	list_for_each_entry_reverse(crtc, &(dev)->mode_config.crtc_list, head)
+
 #endif /* __DRM_CRTC_H__ */