On Wed, Nov 6, 2019 at 12:21 PM Zeng, Oak <Oak.Zeng@xxxxxxx> 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@xxxxxxx>
A few comments below, otherwise looks good to me.
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
> index 555d8e5..8003201 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
> @@ -127,18 +127,43 @@ 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/
apg -> agp
> + * 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
APG -> AGP
> + * 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
> + */
You may want to add a comment that the AGP aperture just maps to
physical bus or IOVA addresses on the platform. It's also used for
page tables in system memory.
> 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.
> + */
> 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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