On Mon, 22 Jun 2015, Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> wrote:
> On Mon, Jun 22, 2015 at 8:02 AM, Daniel Vetter <daniel.vetter@xxxxxxxx> 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?
FWIW i915_drv.h has
#define WARN_ON(x) WARN((x), "WARN_ON(" #x ")")
which makes it a little better...
BR,
Jani.
>
> josh
>
>> Cc: Yogesh Mohan Marimuthu <yogesh.mohan.marimuthu@xxxxxxxxx>
>> Cc: Gaurav K Singh <gaurav.k.singh@xxxxxxxxx>
>> Cc: Michel Dänzer <michel.daenzer@xxxxxxx>
>> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
>> ---
>> 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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--
Jani Nikula, Intel Open Source Technology Center
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