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

[Deng, Emily]

[AMD Official Use Only - Internal Distribution Only]

>-----Original Message-----
>From: Christian König <ckoenig.leichtzumerken at gmail.com>
>Sent: Tuesday, March 30, 2021 3:13 PM
>To: Deng, Emily <Emily.Deng at amd.com>; amd-gfx at lists.freedesktop.org
>Subject: Re: [PATCH 5/6] drm/amdgpu: Disable RPTR write back for navi12
>
>
>
>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.
Issue occurs, when occurs clockgating, at the same time, the rptr write back occurs. At this time, the utcl2 translation will hang.
>
>>
>> -/* 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);