[PATCH] drm/amdgpu: Set VM_L2_CNTL.PDE_FAULT_CLASSIFICATION to 0

[Bridgman, John]

Or is the idea that we should never see a PDE fault unless something goes wrong, and that we would set up an entry corresponding to an unmapped subtree as an invalid PTE for a very large page rather than an invalid PDE?

Thanks,
John
  Original Message
From: Bridgman, John
Sent: Monday, February 25, 2019 22:46
To: Alex Deucher; Zhao, Yong
Cc: amd-gfx list
Subject: Re: [PATCH] drm/amdgpu: Set VM_L2_CNTL.PDE_FAULT_CLASSIFICATION to 0


Don't we want PDE faults to be treated the same way as page faults? Or am I misinterpreting the commit message?

Thanks,
John
  Original Message
From: Alex Deucher
Sent: Monday, February 25, 2019 21:53
To: Zhao, Yong
Cc: amd-gfx at lists.freedesktop.org
Subject: Re: [PATCH] drm/amdgpu: Set VM_L2_CNTL.PDE_FAULT_CLASSIFICATION to 0


On Mon, Feb 25, 2019 at 6:03 PM Zhao, Yong <Yong.Zhao at amd.com> wrote:
>
> This is recommended by HW designers. Previously when it was set to 1,
> the PDE walk error in VM fault will be treated as
> PERMISSION_OR_INVALID_PAGE_FAULT rather than usually expected OTHER_FAULT.
> As a result, the retry control in VM_CONTEXT*_CNTL will change accordingly.
>
> The above behavior is kind of abnormal. Furthermore, the
> PDE_FAULT_CLASSIFICATION == 1 feature was targeted for very old ASICs
> and it never made it way to production. Therefore, we should set it to 0.
>
> Signed-off-by: Yong Zhao <Yong.Zhao at amd.com>

Acked-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>  drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c | 2 +-
>  drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c b/drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c
> index f5edddf3b29d..c10ed568ca6c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c
> @@ -143,7 +143,7 @@ static void gfxhub_v1_0_init_cache_regs(struct amdgpu_device *adev)
>         /* XXX for emulation, Refer to closed source code.*/
>         tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, L2_PDE0_CACHE_TAG_GENERATION_MODE,
>                             0);
> -       tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, PDE_FAULT_CLASSIFICATION, 1);
> +       tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, PDE_FAULT_CLASSIFICATION, 0);
>         tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, CONTEXT1_IDENTITY_ACCESS_MODE, 1);
>         tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, IDENTITY_MODE_FRAGMENT_SIZE, 0);
>         WREG32_SOC15(GC, 0, mmVM_L2_CNTL, tmp);
> diff --git a/drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c b/drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c
> index d0d966d6080a..2a039946a549 100644
> --- a/drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c
> @@ -163,7 +163,7 @@ static void mmhub_v1_0_init_cache_regs(struct amdgpu_device *adev)
>         /* XXX for emulation, Refer to closed source code.*/
>         tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, L2_PDE0_CACHE_TAG_GENERATION_MODE,
>                             0);
> -       tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, PDE_FAULT_CLASSIFICATION, 1);
> +       tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, PDE_FAULT_CLASSIFICATION, 0);
>         tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, CONTEXT1_IDENTITY_ACCESS_MODE, 1);
>         tmp = REG_SET_FIELD(tmp, VM_L2_CNTL, IDENTITY_MODE_FRAGMENT_SIZE, 0);
>         WREG32_SOC15(MMHUB, 0, mmVM_L2_CNTL, tmp);
> --
> 2.17.1
>
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