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

[Koenig, Christian]

Am 06.11.19 um 21:05 schrieb Zeng, Oak:
> Thanks Alex.
>
>> AGP is also used for page tables in system memory.
> I am not aware of this usage. I thought page table are all in frame buffer today. Was this a use case in old asics?

No, that is pretty new and only works for Renoir. But we have disabled 
it currently because of bad interactions with IOMMU.

Christian.

>
> Oak
>
> -----Original Message-----
> From: Alex Deucher <alexdeucher at gmail.com>
> Sent: Wednesday, November 6, 2019 12:37 PM
> To: Zeng, Oak <Oak.Zeng at amd.com>
> Cc: amd-gfx at lists.freedesktop.org; Kuehling, Felix <Felix.Kuehling at amd.com>; Koenig, Christian <Christian.Koenig at amd.com>
> Subject: Re: [PATCH] drm/amdgpu: Add comments to gmc structure
>
> On Wed, Nov 6, 2019 at 12:21 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>
> 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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