Re: [PATCH v2 2/3] drm/amdgpu: Allow dma_map_sg() coalescing

From: Sinan Kaya <okaya-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>,
	amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org,
	dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
Cc: alexander.deucher-5C7GfCeVMHo@public.gmane.org,
	David1.Zhou-5C7GfCeVMHo@public.gmane.org,
	christian.koenig-5C7GfCeVMHo@public.gmane.org
Subject: Re: [PATCH v2 2/3] drm/amdgpu: Allow dma_map_sg() coalescing
Date: Tue, 17 Apr 2018 17:13:48 -0400	[thread overview]
Message-ID: <59bb29d9-da0c-1542-88bf-71bed96f3ed2@codeaurora.org> (raw)
In-Reply-To: <622c9ac3784170880dbde6900146e68631df958a.1523977133.git.robin.murphy-5wv7dgnIgG8@public.gmane.org>

On 4/17/2018 11:58 AM, Robin Murphy wrote:
> The amdgpu driver doesn't appear to directly use the scatterlist mapped
> by amdgpu_ttm_tt_pin_userptr(), it merely hands it off to
> drm_prime_sg_to_page_addr_arrays() to generate the dma_address array
> which it actually cares about. Now that the latter can cope with
> dma_map_sg() coalescing dma-contiguous segments such that it returns
> 0 < count < nents, we can relax the current count == nents check to
> only consider genuine failure as other drivers do.
> 
> This avoids a false negative on arm64 systems with an IOMMU.
> 
> Reported-by: Sinan Kaya <okaya@codeaurora.org>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> 
> v2: Expand commit message to clarify
> 
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 205da3ff9cd0..f81e96a4242f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -813,7 +813,7 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>  
>  	r = -ENOMEM;
>  	nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
> -	if (nents != ttm->sg->nents)
> +	if (nents == 0)
>  		goto release_sg;
>  
>  	drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
> 

Tested-by: Sinan Kaya <okaya@codeaurora.org>

using QDF2400 and XFX Vega64 GPU for the first two patches.

./builddir/tests/amdgpu/amdgpu_test -s 1

Suite: Basic Tests
  Test: Userptr Test ...passed

Userptr Test fails without this patch.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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