[Intel-gfx] [PATCH 2/2] drm/i915: fix up _wait_for macro

[Daniel Vetter]

On Thu, Mar 28, 2013 at 01:00:56PM +0200, Ville Syrjälä wrote:
> On Thu, Mar 28, 2013 at 12:03:25AM +0100, Daniel Vetter wrote:
> > As Thomas Gleixner spotted, it's rather horrible racy:
> > - We can miss almost a full tick, so need to compensate by 1 jiffy.
> 
> I have a feeling this is a rather common pattern, so I wonder
> if [mu]secs_to_jiffies() should do the +1 already for everyone.
> Or maybe there should be some other macros for specifying
> timeouts that would do the +1.
> 
> > - We need to re-check the condition when having timed-out, since a
> >   the last check could have been before the timeout expired. E.g. when
> >   we've been preempted or a long irq happened.
> > 
> > Cc: Thomas Gleixner <tglx at linutronix.de>
> > Reported-by: Jack Winter <jbh at alchemy.lu>
> > Cc: Jack Winter <jbh at alchemy.lu>
> > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Merged both patches, thanks for the review.
-Daniel

> 
> > ---
> >  drivers/gpu/drm/i915/intel_drv.h | 13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index c8c1979..9dcae4e 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -33,12 +33,21 @@
> >  #include <drm/drm_fb_helper.h>
> >  #include <drm/drm_dp_helper.h>
> >  
> > +/**
> > + * _wait_for - magic (register) wait macro
> > + *
> > + * Does the right thing for modeset paths when run under kdgb or similar atomic
> > + * contexts. Note that it's important that we check the condition again after
> > + * having timed out, since the timeout could be due to preemption or similar and
> > + * we've never had a chance to check the condition before the timeout.
> > + */
> >  #define _wait_for(COND, MS, W) ({ \
> > -	unsigned long timeout__ = jiffies + msecs_to_jiffies(MS);	\
> > +	unsigned long timeout__ = jiffies + msecs_to_jiffies(MS) + 1;	\
> >  	int ret__ = 0;							\
> >  	while (!(COND)) {						\
> >  		if (time_after(jiffies, timeout__)) {			\
> > -			ret__ = -ETIMEDOUT;				\
> > +			if (!(COND))					\
> > +				ret__ = -ETIMEDOUT;			\
> >  			break;						\
> >  		}							\
> >  		if (W && drm_can_sleep())  {				\
> > -- 
> > 1.7.11.7
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ville Syrjälä
> Intel OTC

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch