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

[liuxinliang <z.liuxinliang@xxxxxxxxxxxxx>]

On 2017/2/25 9:39, liuxinliang wrote:
> 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@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 | 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);
And put this line in CONFIG_DRM_FBDEV_EMULATION
> > +
> >       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;
And here.

-xinliang

> >   };
> >     extern const struct kirin_dc_ops ade_dc_ops;


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