Update: UVD status on loongson 3a platform

cee1 fykcee1 at gmail.com
Thu Sep 5 20:19:08 PDT 2013

2013/9/6 Jerome Glisse <j.glisse at gmail.com>:
> On Thu, Sep 05, 2013 at 10:14:32PM +0800, Chen Jie wrote:
>> Hi all,
>> This thread is about
>> http://lists.freedesktop.org/archives/dri-devel/2013-April/037598.html.
>> We recently find some interesting thing about UVD based playback on
>> loongson 3a plaform, and also find a way to fix the problem.
>> First, we find memcpy in [mesa]src/gallium/drivers/radeon/radeon_uvd.c
>> caused the problem:
>> * If memcpy is implemented though 16B or 8B load/store instructions,
>> it will normally caused video mosaic. When insert a memcmp after the
>> copying code in memcpy, it will report the src and dest are not equal.
>> * If memcpy use 1B load/store instructions only, the memcmp after the
>> copying code reports equal.
>> Then we find the following changeset fixs out problem:
>> diff --git a/src/gallium/drivers/radeon/radeon_uvd.c
>> b/src/gallium/drivers/radeon/radeon_uvd.c
>> index 2f98de2..f9599b6 100644
>> --- a/src/gallium/drivers/radeon/radeon_uvd.c
>> +++ b/src/gallium/drivers/radeon/radeon_uvd.c
>> @@ -162,7 +162,7 @@ static bool create_buffer(struct ruvd_decoder *dec,
>>    unsigned size)
>>  {
>>   buffer->buf = dec->ws->buffer_create(dec->ws, size, 4096, false,
>>   if (!buffer->buf)
>>   return false;
>> The VRAM is mapped to an uncached area in out platform, so, my
>> question is what could go wrong while using  >4B load/store
>> instructions in UVD workflow? Any idea?
> How do you map the VRAM into user process mapping ? ie do you have
> something like Intel PAT or something like MTRR or something else.
> In other word, can you map into process address space a region of
> io memory (GPU VRAM in this case) and mark it as uncached so that
> none of the access to it goes through CPU cache.
Yes, of course.

On mips, there's a specific range of address space that is used to
access IO memory directly, and the address of VRAM BOs is just in this


- cee1

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