Re: [PATCH 4/6] drm/radeon: Add a rmb() in IH processing

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2011-07-15 at 04:19 +0000, Matt Turner wrote:
> On Wed, Jul 13, 2011 at 6:28 AM, Benjamin Herrenschmidt
> <benh@kernel.crashing.org> wrote:
> > We should have a read memory barrier between reading the WPTR from
> > memory and reading ring entries based on that value (ie, we need to
> > ensure both loads are done in order by the CPU).
> >
> > It could be argued that the MMIO reads in r600_ack_irq() might be
> > enough to get that barrier but I prefer keeping an explicit one just
> > in case.
> >
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> >
> > (resent adding dri-devel to the CC list to hit patchwork)
> >
> > drivers/gpu/drm/radeon/r600.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
> > index 3c86b15..7e5c801 100644
> > --- a/drivers/gpu/drm/radeon/r600.c
> > +++ b/drivers/gpu/drm/radeon/r600.c
> > @@ -3312,6 +3312,9 @@ int r600_irq_process(struct radeon_device *rdev)
> >        }
> >
> >  restart_ih:
> > +       /* Order reading of wptr vs. reading of IH ring data */
> > +       wmb();
> > +
> >        /* display interrupts */
> >        r600_irq_ack(rdev);
> 
> The subject line says rmb(), but this says wmb(). Just want to verify
> what you have is correct.

Nice spotting, it's a typo and should have been rmb(). I'll fix it and
respin.

Cheers,
Ben