[radeon]Question about create ring BO in VRAM

[Alex Deucher]

On Fri, Nov 4, 2011 at 10:26 AM, Chen Jie <chenj at lemote.com> wrote:
> Hi all,
>
> I tried to create/pin ring BO in VRAM instead of GTT to debug some
> ring-related problems. After I did this, it rendered a black screen in
> X (on a X86 RS780E board), but radeon.test passed.
> 'ps aux' shows X uninterruptibly sleeps on radeon.
>
> Curious why this does not work?

The tricky part is dealing with the HDP cache.  Access to vram via the
PCI FB BAR goes through the HDP cache, you have to make sure it's
flushed properly before the GPU starts using the data there.  To flush
it, either read back from vram, or write 1 to the
HDP_MEM_COHERENCY_FLUSH_CNTL register.  We generally don't recommend
putting the ring in vram.

Alex

>
>
>
> Regards,
> -- Chen Jie
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