[PATCH] drm/amdgpu: use ttm pool first

[Chunming Zhou]

On 2018年01月24日 17:43, Christian König wrote:
> Am 24.01.2018 um 10:17 schrieb Chunming Zhou:
>> dma path is low than ttm pool.
>
> That won't work correctly in some cases.
>
>> Question:
>> But why need two path? What spicific problem can be solved by dma path?
>
> That is mostly for ARM and some (rare) x86 platforms without IOMMU 
> where some memory is above the 40bit limit in the PCIe address space.
>
> Our GPUs can unfortunately only deal with 40bits of address space, so 
> on those systems we need to go the slow path and make sure that we 
> don't try to touch that high memory.
>
> What we could really improve is the detection using swiotlb_nr_tbl(), 
> cause that is actually completely wrong.
OK, the patch is trying to use ttm pool first, if dma_map_page fails, 
then fallback to swtlb path, is that ok?

Regards,
David Zhou
>
> Regards,
> Christian.
>
>>
>> Change-Id: I4a9fc7103658e643f33e267616fc69743b20b09e
>> Signed-off-by: Chunming Zhou <david1.zhou at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> index d32f48259c40..8d8a616bf4f5 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> @@ -996,6 +996,7 @@ static int amdgpu_ttm_tt_populate(struct ttm_tt 
>> *ttm,
>>       struct amdgpu_device *adev = amdgpu_ttm_adev(ttm->bdev);
>>       struct amdgpu_ttm_tt *gtt = (void *)ttm;
>>       bool slave = !!(ttm->page_flags & TTM_PAGE_FLAG_SG);
>> +    int r;
>>         if (ttm->state != tt_unpopulated)
>>           return 0;
>> @@ -1017,13 +1018,14 @@ static int amdgpu_ttm_tt_populate(struct 
>> ttm_tt *ttm,
>>           return 0;
>>       }
>>   +    r = ttm_populate_and_map_pages(adev->dev, &gtt->ttm, ctx);
>> +
>>   #ifdef CONFIG_SWIOTLB
>> -    if (swiotlb_nr_tbl()) {
>> -        return ttm_dma_populate(&gtt->ttm, adev->dev, ctx);
>> +    if ((r == -EFAULT) && swiotlb_nr_tbl()) {
>> +        r = ttm_dma_populate(&gtt->ttm, adev->dev, ctx);
>>       }
>>   #endif
>> -
>> -    return ttm_populate_and_map_pages(adev->dev, &gtt->ttm, ctx);
>> +    return r;
>>   }
>>     static void amdgpu_ttm_tt_unpopulate(struct ttm_tt *ttm)
>
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