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

[Alex Deucher]

On Wed, Jul 13, 2011 at 10:44 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
> 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>

evergreen.c will need a similar fix.

Alex

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