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Subject[PATCH 4.9 91/92] drm: rcar-du: Fix race condition when disabling planes at CRTC stop
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

commit 641307df71fe77d7b38a477067495ede05d47295 upstream.

When stopping the CRTC the driver must disable all planes and wait for
the change to take effect at the next vblank. Merely calling
drm_crtc_wait_one_vblank() is not enough, as the function doesn't
include any mechanism to handle the race with vblank interrupts.

Replace the drm_crtc_wait_one_vblank() call with a manual mechanism that
handles the vblank interrupt race.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: thongsyho <thong.ho.px@rvc.renesas.com>
Signed-off-by: Nhan Nguyen <nhan.nguyen.yb@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 53 +++++++++++++++++++++++++++++----
drivers/gpu/drm/rcar-du/rcar_du_crtc.h | 8 ++++
2 files changed, 55 insertions(+), 6 deletions(-)

--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
@@ -392,6 +392,31 @@ static void rcar_du_crtc_start(struct rc
rcrtc->started = true;
}

+static void rcar_du_crtc_disable_planes(struct rcar_du_crtc *rcrtc)
+{
+ struct rcar_du_device *rcdu = rcrtc->group->dev;
+ struct drm_crtc *crtc = &rcrtc->crtc;
+ u32 status;
+ /* Make sure vblank interrupts are enabled. */
+ drm_crtc_vblank_get(crtc);
+ /*
+ * Disable planes and calculate how many vertical blanking interrupts we
+ * have to wait for. If a vertical blanking interrupt has been triggered
+ * but not processed yet, we don't know whether it occurred before or
+ * after the planes got disabled. We thus have to wait for two vblank
+ * interrupts in that case.
+ */
+ spin_lock_irq(&rcrtc->vblank_lock);
+ rcar_du_group_write(rcrtc->group, rcrtc->index % 2 ? DS2PR : DS1PR, 0);
+ status = rcar_du_crtc_read(rcrtc, DSSR);
+ rcrtc->vblank_count = status & DSSR_VBK ? 2 : 1;
+ spin_unlock_irq(&rcrtc->vblank_lock);
+ if (!wait_event_timeout(rcrtc->vblank_wait, rcrtc->vblank_count == 0,
+ msecs_to_jiffies(100)))
+ dev_warn(rcdu->dev, "vertical blanking timeout\n");
+ drm_crtc_vblank_put(crtc);
+}
+
static void rcar_du_crtc_stop(struct rcar_du_crtc *rcrtc)
{
struct drm_crtc *crtc = &rcrtc->crtc;
@@ -400,17 +425,16 @@ static void rcar_du_crtc_stop(struct rca
return;

/* Disable all planes and wait for the change to take effect. This is
- * required as the DSnPR registers are updated on vblank, and no vblank
- * will occur once the CRTC is stopped. Disabling planes when starting
- * the CRTC thus wouldn't be enough as it would start scanning out
- * immediately from old frame buffers until the next vblank.
+ * required as the plane enable registers are updated on vblank, and no
+ * vblank will occur once the CRTC is stopped. Disabling planes when
+ * starting the CRTC thus wouldn't be enough as it would start scanning
+ * out immediately from old frame buffers until the next vblank.
*
* This increases the CRTC stop delay, especially when multiple CRTCs
* are stopped in one operation as we now wait for one vblank per CRTC.
* Whether this can be improved needs to be researched.
*/
- rcar_du_group_write(rcrtc->group, rcrtc->index % 2 ? DS2PR : DS1PR, 0);
- drm_crtc_wait_one_vblank(crtc);
+ rcar_du_crtc_disable_planes(rcrtc);

/* Disable vertical blanking interrupt reporting. We first need to wait
* for page flip completion before stopping the CRTC as userspace
@@ -548,10 +572,25 @@ static irqreturn_t rcar_du_crtc_irq(int
irqreturn_t ret = IRQ_NONE;
u32 status;

+ spin_lock(&rcrtc->vblank_lock);
+
status = rcar_du_crtc_read(rcrtc, DSSR);
rcar_du_crtc_write(rcrtc, DSRCR, status & DSRCR_MASK);

if (status & DSSR_VBK) {
+ /*
+ * Wake up the vblank wait if the counter reaches 0. This must
+ * be protected by the vblank_lock to avoid races in
+ * rcar_du_crtc_disable_planes().
+ */
+ if (rcrtc->vblank_count) {
+ if (--rcrtc->vblank_count == 0)
+ wake_up(&rcrtc->vblank_wait);
+ }
+ }
+ spin_unlock(&rcrtc->vblank_lock);
+
+ if (status & DSSR_VBK) {
drm_crtc_handle_vblank(&rcrtc->crtc);
rcar_du_crtc_finish_page_flip(rcrtc);
ret = IRQ_HANDLED;
@@ -606,6 +645,8 @@ int rcar_du_crtc_create(struct rcar_du_g
}

init_waitqueue_head(&rcrtc->flip_wait);
+ init_waitqueue_head(&rcrtc->vblank_wait);
+ spin_lock_init(&rcrtc->vblank_lock);

rcrtc->group = rgrp;
rcrtc->mmio_offset = mmio_offsets[index];
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
@@ -15,6 +15,7 @@
#define __RCAR_DU_CRTC_H__

#include <linux/mutex.h>
+#include <linux/spinlock.h>
#include <linux/wait.h>

#include <drm/drmP.h>
@@ -33,6 +34,9 @@ struct rcar_du_vsp;
* @started: whether the CRTC has been started and is running
* @event: event to post when the pending page flip completes
* @flip_wait: wait queue used to signal page flip completion
+ * @vblank_lock: protects vblank_wait and vblank_count
+ * @vblank_wait: wait queue used to signal vertical blanking
+ * @vblank_count: number of vertical blanking interrupts to wait for
* @outputs: bitmask of the outputs (enum rcar_du_output) driven by this CRTC
* @group: CRTC group this CRTC belongs to
*/
@@ -48,6 +52,10 @@ struct rcar_du_crtc {
struct drm_pending_vblank_event *event;
wait_queue_head_t flip_wait;

+ spinlock_t vblank_lock;
+ wait_queue_head_t vblank_wait;
+ unsigned int vblank_count;
+
unsigned int outputs;

struct rcar_du_group *group;

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