[PATCH 5/6] drm/radeon: Do an MMIO read on interrupts when not uisng MSIs

[Alex Deucher]

On Wed, Jul 13, 2011 at 2:28 AM, Benjamin Herrenschmidt
<benh at kernel.crashing.org> wrote:
> When not using MSIs, there is no guarantee that DMA from the device
> has been fully flushed to point where it's visible to the CPU when
> taking an interrupt. To get this guarantee, we need to perform an
> MMIO read from the device, which will flush all outstanding DMAs
> from bridges between the device and the system.
>
> 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 |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
> index 7e5c801..25b2dab 100644
> --- a/drivers/gpu/drm/radeon/r600.c
> +++ b/drivers/gpu/drm/radeon/r600.c
> @@ -3300,6 +3300,10 @@ int r600_irq_process(struct radeon_device *rdev)
>        if (!rdev->ih.enabled || rdev->shutdown)
>                return IRQ_NONE;
>
> +       /* No MSIs, need a dummy read to flush PCI DMAs */
> +       if (!rdev->msi_enabled)
> +               RREG32(IH_RB_WPTR);
> +
>        wptr = r600_get_ih_wptr(rdev);
>        rptr = rdev->ih.rptr;
>        DRM_DEBUG("r600_irq_process start: rptr %d, wptr %d\n", rptr, wptr);
>
>
>
>