[Intel-gfx] [PATCH] drm/vblank: WARN_ON nested use of drm_vblank_on/off

[Josh Boyer]

On Mon, Jun 22, 2015 at 8:02 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> We should never nest these since in theory kms drivers should know
> when a pipe is on/off and call the corresponding enable/disable
> functions for the vblank helper code only once. But for historical
> reasons (the shared-with-ums version of this code in modeset_pre/post
> needed to be able to cope with silly userspace that lost track of
> things) we still have this bit of "robustness" around.
>
> Enforce this with a WARN_ON, preparing to eventually rip out this
> special handling.

This doesn't really provide any context in the WARN_ON itself.  It
will just result in a splat that looks like a kernel oops, and end
users and distribution maintainers will be left scratching their
heads.

Could this be done with a printk warning instead, or could you at
least provide a pr_warn statement to help people understand why their
machine has an oops splat?

josh

> Cc: Yogesh Mohan Marimuthu <yogesh.mohan.marimuthu at intel.com>
> Cc: Gaurav K Singh <gaurav.k.singh at intel.com>
> Cc: Michel Dänzer <michel.daenzer at amd.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  drivers/gpu/drm/drm_irq.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index f9cc68fbd2a3..3819465abe22 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -1219,6 +1219,8 @@ void drm_vblank_off(struct drm_device *dev, int crtc)
>         vblank_disable_and_save(dev, crtc);
>         wake_up(&vblank->queue);
>
> +       WARN_ON(vblank->inmodeset);
> +
>         /*
>          * Prevent subsequent drm_vblank_get() from re-enabling
>          * the vblank interrupt by bumping the refcount.
> @@ -1318,6 +1320,8 @@ void drm_vblank_on(struct drm_device *dev, int crtc)
>                 return;
>
>         spin_lock_irqsave(&dev->vbl_lock, irqflags);
> +       WARN_ON(!vblank->inmodeset);
> +
>         /* Drop our private "prevent drm_vblank_get" refcount */
>         if (vblank->inmodeset) {
>                 atomic_dec(&vblank->refcount);
> --
> 2.1.4
>
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