Re: [RFC][PATCH] drm: kirin: Add a mutex to avoid fb initialization race

From: liuxinliang
Date: Thu Feb 23 2017 - 20:56:41 EST

Hi John,

On 2017/2/23 8:56, John Stultz wrote:
In some cases I've been seeing a race where two framebuffers
would be initialized, as kirin_fbdev_output_poll_changed()
might get called quickly in succession, resulting in the fb
initialization happening twice. This could cause the system

I might understand this race. This because two places call drm_helper_hpd_irq_event might cause the race:
One place is here
static int kirin_drm_kms_init(struct drm_device *dev)
/* force detection after connectors init */

another is the adv7533 interrupt thread handler
static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd)
if (process_hpd && irq0 & ADV7511_INT0_HPD && adv7511->bridge.encoder)


I don't get a better way to fix this yet , I like to put fb_lock into kirin_drm_private.
And it seems hard to fix this in the core drm_helper_hpd_irq_event.


to boot up with a blank screen.

This patch adds a simple mutex to serialize it and seems to
avoid the race.

Obviously I suspect this patch isn't the best solution, but
I wanted to send it out as something concrete to discuss the

Suggestions or feedback for a better solution would be greatly

Cc: Xinliang Liu <z.liuxinliang@xxxxxxxxxxxxx>
Cc: Rongrong Zou <zourongrong@xxxxxxxxx>
Cc: Xinwei Kong <kong.kongxinwei@xxxxxxxxxxxxx>
Cc: Chen Feng <puck.chen@xxxxxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
index ebd5f4f..80c607f 100644
--- a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
+++ b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
@@ -50,11 +50,13 @@ static int kirin_drm_kms_cleanup(struct drm_device *dev)
return 0;
+static DEFINE_MUTEX(fb_lock);
static void kirin_fbdev_output_poll_changed(struct drm_device *dev)
struct kirin_drm_private *priv = dev->dev_private;
+ mutex_lock(&fb_lock);
if (priv->fbdev) {
} else {
@@ -64,6 +66,7 @@ static void kirin_fbdev_output_poll_changed(struct drm_device *dev)
if (IS_ERR(priv->fbdev))
priv->fbdev = NULL;
+ mutex_unlock(&fb_lock);