[PATCH] drm/amdgpu: Add comments to gmc structure

[Alex Deucher]

On Wed, Nov 6, 2019 at 12:27 PM Zeng, Oak <Oak.Zeng at amd.com> wrote:
>
> Explain fields like aper_base, agp_start etc. The definition
> of those fields are confusing as they are from different view
> (CPU or GPU). Add comments for easier understand.
>
> Change-Id: I02c2a27cd0dbc205498eb86aafa722f2e0c25fe6
> Signed-off-by: Oak Zeng <Oak.Zeng at amd.com>

Same comments as the previous version.  With those addressed,
Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
> index 555d8e5..1356ff9 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
> @@ -127,18 +127,44 @@ struct amdgpu_xgmi {
>  };
>
>  struct amdgpu_gmc {
> +       /* FB's physical address in MMIO space (for CPU to
> +        * map FB). This is different compared to the apg/
> +        * gart/vram_start/end field as the later is from
> +        * GPU's view and aper_base is from CPU's view.
> +        */
>         resource_size_t         aper_size;
>         resource_size_t         aper_base;
>         /* for some chips with <= 32MB we need to lie
>          * about vram size near mc fb location */
>         u64                     mc_vram_size;
>         u64                     visible_vram_size;
> +       /* APG aperture start and end in MC address space
> +        * Driver find a hole in the MC address space
> +        * to place AGP by setting MC_VM_AGP_BOT/TOP registers
> +        * Under VMID0, logical address == MC address
> +        * AGP aperture is used to simulate FB in ZFB case
> +        */
>         u64                     agp_size;
>         u64                     agp_start;
>         u64                     agp_end;
> +       /* GART aperture start and end in MC address space
> +        * Driver find a hole in the MC address space
> +        * to place GART by setting VM_CONTEXT0_PAGE_TABLE_START/END_ADDR
> +        * registers
> +        * Under VMID0, logical address inside GART aperture will
> +        * be translated through gpuvm gart page table to access
> +        * paged system memory
> +        */
>         u64                     gart_size;
>         u64                     gart_start;
>         u64                     gart_end;
> +       /* Frame buffer aperture of this GPU device. Different from
> +        * fb_start (see below), this only covers the local GPU device.
> +        * Driver get fb_start from MC_VM_FB_LOCATION_BASE (set by vbios)
> +        * and calculate vram_start of this local device by adding an
> +        * offset inside the XGMI hive.
> +        * Under VMID0, logical address == MC address
> +        */
>         u64                     vram_start;
>         u64                     vram_end;
>         /* FB region , it's same as local vram region in single GPU, in XGMI
> --
> 2.7.4
>
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