[RFC][PATCH v2] drm: kirin: Add a mutex to avoid fb initialization race

[liuxinliang]

Hi John,

The patch seems good to me, except one minus comment.
Maybe change fb_lock to fbdev_lock would be better.

Thanks,
-xinliang

On 2017/2/25 9:25, 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
> initialization happening twice. This could cause the system
> to boot up with a blank screen.
>
> This patch adds a simple mutex to serialize it and seems to
> avoid the race.
>
> Suggestions or feedback would be greatly appreciated!
>
> Cc: Xinliang Liu <z.liuxinliang at hisilicon.com>
> Cc: Rongrong Zou <zourongrong at gmail.com>
> Cc: Xinwei Kong <kong.kongxinwei at hisilicon.com>
> Cc: Chen Feng <puck.chen at hisilicon.com>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Sean Paul <seanpaul at chromium.org>
> Cc: dri-devel at lists.freedesktop.org
> Signed-off-by: John Stultz <john.stultz at linaro.org>
> ---
>   drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c | 4 ++++
>   drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.h | 1 +
>   2 files changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
> index 7ec93ae..b83556a 100644
> --- a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
> +++ b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
> @@ -55,6 +55,7 @@ static void kirin_fbdev_output_poll_changed(struct drm_device *dev)
>   {
>   	struct kirin_drm_private *priv = dev->dev_private;
>   
> +	mutex_lock(&priv->fb_lock);
>   	if (priv->fbdev) {
>   		drm_fbdev_cma_hotplug_event(priv->fbdev);
>   	} else {
> @@ -63,6 +64,7 @@ static void kirin_fbdev_output_poll_changed(struct drm_device *dev)
>   		if (IS_ERR(priv->fbdev))
>   			priv->fbdev = NULL;
>   	}
> +	mutex_unlock(&priv->fb_lock);
>   }
>   #endif
>   
> @@ -95,6 +97,8 @@ static int kirin_drm_kms_init(struct drm_device *dev)
>   	if (!priv)
>   		return -ENOMEM;
>   
> +	mutex_init(&priv->fb_lock);
> +
>   	dev->dev_private = priv;
>   	dev_set_drvdata(dev->dev, dev);
>   
> diff --git a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.h b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.h
> index 7f60c649..9b6d2b1 100644
> --- a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.h
> +++ b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.h
> @@ -23,6 +23,7 @@ struct kirin_drm_private {
>   #ifdef CONFIG_DRM_FBDEV_EMULATION
>   	struct drm_fbdev_cma *fbdev;
>   #endif
> +	struct mutex fb_lock;
>   };
>   
>   extern const struct kirin_dc_ops ade_dc_ops;