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

[Ville Syrjälä]

On Tue, Feb 09, 2016 at 02:29:49PM +0100, Mario Kleiner wrote:
> 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 at gmail.com>
> >>> Cc: <stable at vger.kernel.org> # 3.18+
> >>> Cc: michel at daenzer.net
> >>> Cc: vbabka at suse.cz
> >>> Cc: ville.syrjala at linux.intel.com
> >>> Cc: daniel.vetter at ffwll.ch
> >>> Cc: dri-devel at lists.freedesktop.org
> >>> Cc: alexander.deucher at amd.com
> >>> Cc: christian.koenig at 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 at 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.

Yeah, just offdelay==0 seems best. Otherwise I think we could actually
leave the interrupt enabled indefinitely w/ offdelay>0 since there's not
going to be a drm_vblank_put() to arm the disable timer.

> 
> -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
> >

-- 
Ville Syrjälä
Intel OTC