Re: [PATCH 4/6] drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on()

[Mario Kleiner <mario.kleiner.de@gmail.com>]

On 02/09/2016 12:10 PM, Ville Syrjälä wrote:
> On Tue, Feb 09, 2016 at 11:06:18AM +0100, Daniel Vetter wrote:
>> On Mon, Feb 08, 2016 at 02:13:27AM +0100, Mario Kleiner wrote:
>>> drm_vblank_offdelay can have three different types of values:
>>>
>>> < 0 is to be always treated the same as dev->vblank_disable_immediate
>>> = 0 is to be treated as "never disable vblanks"
>>>> 0 is to be treated as disable immediate if kms driver wants it
>>>      that way via dev->vblank_disable_immediate. Otherwise it is
>>>      a disable timeout in msecs.
>>>
>>> This got broken in Linux 3.18+ for the implementation of
>>> drm_vblank_on. If the user specified a value of zero which should
>>> always reenable vblank irqs in this function, a kms driver could
>>> override the users choice by setting vblank_disable_immediate
>>> to true. This patch fixes the regression and keeps the user in
>>> control.
>>>
>>> Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
>>> Cc: <stable@vger.kernel.org> # 3.18+
>>> Cc: michel@daenzer.net
>>> Cc: vbabka@suse.cz
>>> Cc: ville.syrjala@linux.intel.com
>>> Cc: daniel.vetter@ffwll.ch
>>> Cc: dri-devel@lists.freedesktop.org
>>> Cc: alexander.deucher@amd.com
>>> Cc: christian.koenig@amd.com
>>> ---
>>>   drivers/gpu/drm/drm_irq.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
>>> index 5c27ad3..fb17c45 100644
>>> --- a/drivers/gpu/drm/drm_irq.c
>>> +++ b/drivers/gpu/drm/drm_irq.c
>>> @@ -1492,8 +1492,8 @@ void drm_vblank_on(struct drm_device *dev, unsigned int pipe)
>>>   	 * re-enable interrupts if there are users left, or the
>>>   	 * user wishes vblank interrupts to be enabled all the time.
>>>   	 */
>>> -	if (atomic_read(&vblank->refcount) != 0 ||
>>> -	    (!dev->vblank_disable_immediate && drm_vblank_offdelay == 0))
>>> +	if (atomic_read(&vblank->refcount) != 0 || drm_vblank_offdelay == 0 ||
>>> +	    (!dev->vblank_disable_immediate && drm_vblank_offdelay > 0))
>>
>> Hm, shouldn't we change this to only enable the vblank irq if we need it,
>> i.e. offdelay == 0? For delayed disabling there's kinda no need to enable
>> it superflously after a modeset, if userspace didn't yet ask for vblank
>> timestamps. But then is was specifically added by Ville in cd19e52aee922,
>> so I guess someone really wants this.
>
> IIRC what I wanted was to just re-enable the interrupt for the offdelay==0
> case. I think it just ended up as a mess due to changing some of the
> semantics of offdelay<0 vs. offdelay==0 vs. disable_immediate during the
> review of the series. So yeah, given how drm_vblank_put() works now, I'd
> just make this check for offdelay==0.
>
>>
>> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>

I can change that to offdelay==0 only, if you want. It was mostly about 
preserving what's there while at the same time fixing the important 
offdelay==0 user override.

-mario

>>>   		WARN_ON(drm_vblank_enable(dev, pipe));
>>>   	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
>>>   }
>>> --
>>> 1.9.1
>>>
>>
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> http://blog.ffwll.ch
>