r600_dma_ring_test() failed - synchronization problem with write-combining memory

[Christian König]

Am 10.10.2014 um 18:02 schrieb Alex Deucher:
> On Fri, Oct 10, 2014 at 12:00 PM, Alex Deucher <alexdeucher at gmail.com> wrote:
>> On Thu, Oct 9, 2014 at 3:10 PM, Alexander Fyodorov <halcy at yandex.ru> wrote:
>>> 09.10.2014, 22:32, "Christian König" <christian.koenig at amd.com>:
>>>> Am 09.10.2014 um 20:15 schrieb Alexander Fyodorov:
>>>>>   09.10.2014, 21:42, "Christian König" <christian.koenig at amd.com>:
>>>>>>   For VRAM it is true that we have a couple of different caches between
>>>>>>   the CPU and the actually memory, which need to be flushed explicitly if
>>>>>>   you want to see a value written by the GPU.
>>>>>   Then maybe such a flush is what I need. How do I put it in the instruction ring buffer?
>>>> At least we need to flush the HDP, but what hardware generation is this
>>>> exactly? Some R6xx don't support hardware flushes in the ring buffer.
>>> I observed the problem on HD2400 and HD6670.
>>>
>>>> Try to call r600_mmio_hdp_flush(rdev) from the loop which checks the
>>>> value written.
>>> Yep, it helped. Here is the patch against 3.10.53, tested on HD2400.
>>>
>>>
>>> Flush VRAM cache before each read when polling.
>>>
>>> Signed-off-by: Alexander Fyodorov <halcy at yandex.ru>
>>>
>>>
>>> Index: drivers/gpu/drm/radeon/r600.c
>>> ===================================================================
>>> --- drivers/gpu/drm/radeon/r600.c       (revision 11647)
>>> +++ drivers/gpu/drm/radeon/r600.c       (working copy)
>>> @@ -2899,6 +2899,7 @@
>>>          radeon_ring_unlock_commit(rdev, ring);
>>>
>>>          for (i = 0; i < rdev->usec_timeout; i++) {
>>> +               r600_ioctl_wait_idle(rdev, rdev->vram_scratch.robj);
>>>                  tmp = readl(ptr);
>>>                  if (tmp == 0xDEADBEEF)
>>>                          break;
>> I think I'd prefer to just switch the test to use gart memory since
>> this code is shared by different asics thay may not all implement hdp
>> flush the same way.  We can just reserve a couple of slots in the wb
>> page.

Works for me as well. We could also grab a few bytes of GART using the 
SA manager.

> Also newer versions of the test will need a similar fix.

See the patch I already send to you, the SDMA on CIK is the only one not 
usign this ring test.

Christian.

>
> Alex