This is a note to let you know that I've just added the patch titled
drm: rcar-du: Fix race condition when disabling planes at CRTC stop
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: drm-rcar-du-fix-race-condition-when-disabling-planes-at-crtc-stop.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 641307df71fe77d7b38a477067495ede05d47295 Mon Sep 17 00:00:00 2001
From: Laurent Pinchart laurent.pinchart+renesas@ideasonboard.com Date: Sat, 29 Jul 2017 02:31:33 +0300 Subject: drm: rcar-du: Fix race condition when disabling planes at CRTC stop
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 | 54 +++++++++++++++++++++++++++++---- drivers/gpu/drm/rcar-du/rcar_du_crtc.h | 8 ++++ 2 files changed, 56 insertions(+), 6 deletions(-)
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c @@ -371,6 +371,31 @@ 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; @@ -379,17 +404,16 @@ 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 @@ -528,10 +552,26 @@ 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_handle_vblank(rcrtc->crtc.dev, rcrtc->index); rcar_du_crtc_finish_page_flip(rcrtc); ret = IRQ_HANDLED; @@ -585,6 +625,8 @@ 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> @@ -32,6 +33,9 @@ struct rcar_du_group; * @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 * @enabled: whether the CRTC is enabled, used to control system resume * @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; bool enabled;
Patches currently in stable-queue which might be from laurent.pinchart+renesas@ideasonboard.com are
queue-4.4/drm-rcar-du-use-the-vbk-interrupt-for-vblank-events.patch queue-4.4/drm-rcar-du-fix-race-condition-when-disabling-planes-at-crtc-stop.patch