[RFC PATCH] drm/exynos: fix pending update handling

[Andrzej Hajda]

Exynos DRM devices update their registers at vblank time. Exynos-DRM uses
custom mechanism to wait for vblank. This mechanism is error prone -
variables are not updated atomically. As a result in certain circumstances
user space can try to free buffers which are still in use by hardware,
in such cases IOMMU can throw OOPS.
The patch instead of fixing the mechanism replaces it with drm core helper.

Signed-off-by: Andrzej Hajda <a.hajda at samsung.com>
---
Hi Tobias,

This is a quick/dirty patch just for checking if it solves your issue.
Successfully tested on decon5433/dsi/i80 path.

Please verify if it helps in your case.

The patch is based on exynos-drm-next and
"drm/exynos: fix cancel page flip code" [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel.samsung-soc/53801

Regards
Andrzej
---
 drivers/gpu/drm/exynos/exynos_drm_crtc.c | 16 +-----------
 drivers/gpu/drm/exynos/exynos_drm_drv.c  | 44 +-------------------------------
 drivers/gpu/drm/exynos/exynos_drm_drv.h  |  2 --
 3 files changed, 2 insertions(+), 60 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
index 785ffa6..5b6845b 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
@@ -134,8 +134,6 @@ struct exynos_drm_crtc *exynos_drm_crtc_create(struct drm_device *drm_dev,
 	exynos_crtc->ops = ops;
 	exynos_crtc->ctx = ctx;
 
-	init_waitqueue_head(&exynos_crtc->wait_update);
-
 	crtc = &exynos_crtc->base;
 
 	private->crtc[pipe] = crtc;
@@ -175,13 +173,6 @@ void exynos_drm_crtc_disable_vblank(struct drm_device *dev, unsigned int pipe)
 		exynos_crtc->ops->disable_vblank(exynos_crtc);
 }
 
-void exynos_drm_crtc_wait_pending_update(struct exynos_drm_crtc *exynos_crtc)
-{
-	wait_event_timeout(exynos_crtc->wait_update,
-			   (atomic_read(&exynos_crtc->pending_update) == 0),
-			   msecs_to_jiffies(50));
-}
-
 void exynos_drm_crtc_finish_update(struct exynos_drm_crtc *exynos_crtc,
 				struct exynos_drm_plane *exynos_plane)
 {
@@ -190,9 +181,6 @@ void exynos_drm_crtc_finish_update(struct exynos_drm_crtc *exynos_crtc,
 
 	exynos_plane->pending_fb = NULL;
 
-	if (atomic_dec_and_test(&exynos_crtc->pending_update))
-		wake_up(&exynos_crtc->wait_update);
-
 	spin_lock_irqsave(&crtc->dev->event_lock, flags);
 	if (exynos_crtc->event)
 		drm_crtc_send_vblank_event(crtc, exynos_crtc->event);
@@ -235,10 +223,8 @@ void exynos_drm_crtc_cancel_page_flip(struct drm_crtc *crtc,
 	spin_lock_irqsave(&crtc->dev->event_lock, flags);
 
 	e = exynos_crtc->event;
-	if (e && e->base.file_priv == file) {
+	if (e && e->base.file_priv == file)
 		exynos_crtc->event = NULL;
-		atomic_dec(&exynos_crtc->pending_update);
-	}
 
 	spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
 
diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.c b/drivers/gpu/drm/exynos/exynos_drm_drv.c
index 0281b30..cc96e85 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_drv.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_drv.c
@@ -45,37 +45,11 @@ struct exynos_atomic_commit {
 	u32			crtcs;
 };
 
-static void exynos_atomic_wait_for_commit(struct drm_atomic_state *state)
-{
-	struct drm_crtc_state *crtc_state;
-	struct drm_crtc *crtc;
-	int i, ret;
-
-	for_each_crtc_in_state(state, crtc, crtc_state, i) {
-		struct exynos_drm_crtc *exynos_crtc = to_exynos_crtc(crtc);
-
-		if (!crtc->state->enable)
-			continue;
-
-		ret = drm_crtc_vblank_get(crtc);
-		if (ret)
-			continue;
-
-		exynos_drm_crtc_wait_pending_update(exynos_crtc);
-		drm_crtc_vblank_put(crtc);
-	}
-}
-
 static void exynos_atomic_commit_complete(struct exynos_atomic_commit *commit)
 {
 	struct drm_device *dev = commit->dev;
 	struct exynos_drm_private *priv = dev->dev_private;
 	struct drm_atomic_state *state = commit->state;
-	struct drm_plane *plane;
-	struct drm_crtc *crtc;
-	struct drm_plane_state *plane_state;
-	struct drm_crtc_state *crtc_state;
-	int i;
 
 	drm_atomic_helper_commit_modeset_disables(dev, state);
 
@@ -89,25 +63,9 @@ static void exynos_atomic_commit_complete(struct exynos_atomic_commit *commit)
 	 * have the relevant clocks enabled to perform the update.
 	 */
 
-	for_each_crtc_in_state(state, crtc, crtc_state, i) {
-		struct exynos_drm_crtc *exynos_crtc = to_exynos_crtc(crtc);
-
-		atomic_set(&exynos_crtc->pending_update, 0);
-	}
-
-	for_each_plane_in_state(state, plane, plane_state, i) {
-		struct exynos_drm_crtc *exynos_crtc =
-						to_exynos_crtc(plane->crtc);
-
-		if (!plane->crtc)
-			continue;
-
-		atomic_inc(&exynos_crtc->pending_update);
-	}
-
 	drm_atomic_helper_commit_planes(dev, state, false);
 
-	exynos_atomic_wait_for_commit(state);
+	drm_atomic_helper_wait_for_vblanks(dev, state);
 
 	drm_atomic_helper_cleanup_planes(dev, state);
 
diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.h b/drivers/gpu/drm/exynos/exynos_drm_drv.h
index 561925f..0bb3766 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_drv.h
+++ b/drivers/gpu/drm/exynos/exynos_drm_drv.h
@@ -174,8 +174,6 @@ struct exynos_drm_crtc {
 	enum exynos_drm_output_type	type;
 	unsigned int			pipe;
 	struct drm_pending_vblank_event	*event;
-	wait_queue_head_t		wait_update;
-	atomic_t			pending_update;
 	const struct exynos_drm_crtc_ops	*ops;
 	void				*ctx;
 	struct exynos_drm_clk		*pipe_clk;
-- 
1.9.1