[PATCH 5/6] drm/amdgpu: Disable RPTR write back for navi12

[Christian König]

Am 30.03.21 um 06:41 schrieb Emily Deng:
> It will hit ramdomly sdma hang, and pending on utcl2
> address translation when access the RPTR polling address.
>
> According sdma firmware team mentioned, the RPTR writeback is done by
> hardware automatically, and will hit issue when clock gating occurs. So
> stop using the rptr write back for sdma5.0.
>
> Signed-off-by: Emily Deng <Emily.Deng at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c | 18 ++++++++++++------
>   1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c b/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
> index 920fc6d4a127..63e4a78181b8 100644
> --- a/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
> @@ -298,13 +298,19 @@ static void sdma_v5_0_ring_patch_cond_exec(struct amdgpu_ring *ring,
>    */
>   static uint64_t sdma_v5_0_ring_get_rptr(struct amdgpu_ring *ring)
>   {
> -	u64 *rptr;
> +	struct amdgpu_device *adev = ring->adev;
> +	u64 rptr;
> +	u32 lowbit, highbit;
> +
> +	lowbit = RREG32(sdma_v5_0_get_reg_offset(adev, ring->me, mmSDMA0_GFX_RB_RPTR));
> +	highbit = RREG32(sdma_v5_0_get_reg_offset(adev, ring->me, mmSDMA0_GFX_RB_RPTR_HI));

That won't work like this.

We have the readpointer writeback because we otherwise can't guarantee 
that the two 32bit values read from the registers are coherent.

In other words it can be that the hi rptr is already wrapped around 
while the lo is still the old value.

Why exactly doesn't the writeback work?

Christian.

>   
> -	/* XXX check if swapping is necessary on BE */
> -	rptr = ((u64 *)&ring->adev->wb.wb[ring->rptr_offs]);
> +	rptr = highbit;
> +	rptr = rptr << 32;
> +	rptr |= lowbit;
>   
> -	DRM_DEBUG("rptr before shift == 0x%016llx\n", *rptr);
> -	return ((*rptr) >> 2);
> +	DRM_DEBUG("rptr before shift == 0x%016llx\n", rptr);
> +	return (rptr >> 2);
>   }
>   
>   /**
> @@ -702,7 +708,7 @@ static int sdma_v5_0_gfx_resume(struct amdgpu_device *adev)
>   		WREG32(sdma_v5_0_get_reg_offset(adev, i, mmSDMA0_GFX_RB_RPTR_ADDR_LO),
>   		       lower_32_bits(adev->wb.gpu_addr + wb_offset) & 0xFFFFFFFC);
>   
> -		rb_cntl = REG_SET_FIELD(rb_cntl, SDMA0_GFX_RB_CNTL, RPTR_WRITEBACK_ENABLE, 1);
> +		rb_cntl = REG_SET_FIELD(rb_cntl, SDMA0_GFX_RB_CNTL, RPTR_WRITEBACK_ENABLE, 0);
>   
>   		WREG32(sdma_v5_0_get_reg_offset(adev, i, mmSDMA0_GFX_RB_BASE), ring->gpu_addr >> 8);
>   		WREG32(sdma_v5_0_get_reg_offset(adev, i, mmSDMA0_GFX_RB_BASE_HI), ring->gpu_addr >> 40);