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

[Alex Deucher]

On Wed, Jul 13, 2011 at 2:28 AM, Benjamin Herrenschmidt
<benh at 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 at kernel.crashing.org>

Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>
> (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);
>
>
>
>
>