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

[Alexander Fyodorov]

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;