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

[Felix Kuehling]

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. Why
does Patch 10 only enable that on GFXv9? Is there less benefit on older
chips?

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

See my replies to patch 6 and 8. Other than that, the series is
Acked-by: Felix Kuehling <Felix.Kuehling at 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 at 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.