[PATCH] drm/amdgpu: use ttm pool first

[Christian König]

Am 24.01.2018 um 10:48 schrieb 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?

Nope, as I wrote that won't work. You must improve the detection if we 
need coherent or not coherent allocation.

Regards,
Christian.

>
> 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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>