Re: [PATCH 01/10] drm/amdgpu: use only the lower address space on GMC9

["Christian König" <christian.koenig-5C7GfCeVMHo@public.gmane.org>]

Am 28.08.2018 um 06:21 schrieb zhoucm1:
>
>
> On 2018年08月28日 03:03, Felix Kuehling wrote:
>> The point of this series seems to be to allow access to small system
>> memory BOs (one page) without a GART mapping. I'm guessing that reduces
>> pressure on the GART and removes the need for HDP and TLB flushes.
> I think if adding these explain/reason to comments are better to 
> enable AGP apperture. If that's true, it's really a clever idea.

Well that is one use case. Another one is that we can enable dGPU 
without any VRAM.

That is really important for emulation and early ASIC testing.

>
> Regards,
> David Zhou
>
>> Why
>> does Patch 10 only enable that on GFXv9? Is there less benefit on older
>> chips?

Can easily be enabled on older chips as well, but I haven't yet had time 
to test it.

>>
>> Is this related to your recent changes to allow page tables in system
>> memory?

Yes, as it turned out that otherwise results in a huge bunch of extra 
GART mappings.

Regards,
Christian.

>>
>> See my replies to patch 6 and 8. Other than that, the series is
>> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
>>
>> Regards,
>>    Felix
>>
>>
>> On 2018-08-27 12:53 PM, Christian König wrote:
>>> Only use the lower address space on GMC9 for the system domain.
>>> Otherwise we would need to sign extend GMC addresses.
>>>
>>> Signed-off-by: Christian König <christian.koenig@amd.com>
>>> ---
>>>   drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c | 7 +++----
>>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c 
>>> b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>> index e44b5191735d..d982956c8329 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>> @@ -938,11 +938,10 @@ static int gmc_v9_0_sw_init(void *handle)
>>>       if (r)
>>>           return r;
>>>   -    /* Set the internal MC address mask
>>> -     * This is the max address of the GPU's
>>> -     * internal address space.
>>> +    /* Use only the lower range for the internal MC address mask. 
>>> This is
>>> +     * the max address of the GPU's internal address space.
>>>        */
>>> -    adev->gmc.mc_mask = 0xffffffffffffULL; /* 48 bit MC */
>>> +    adev->gmc.mc_mask = 0x7fffffffffffULL;
>>>         /* set DMA mask + need_dma32 flags.
>>>        * PCIE - can handle 44-bits.
>> _______________________________________________
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>

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