Re: [PATCH 11/14] drm/amdgpu/ih6.0: Use MMIO ACK for retry CAM on IH 6.0

["Kuehling, Felix" <felix.kuehling@amd.com>]

On 2026-07-02 06:23, Christian König wrote:
> On 7/1/26 18:17, Timur Kristóf wrote:
>> The doorbell is not working on Navi 31.
>> Use the IH_RETRY_CAM_ACK register.
>>
>> Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
> Acked-by: Christian König <christian.koenig@amd.com>
>
> I still haven't found any explanation why we use a doorbell for the CAM in the first place? Lijo, Alex, Felix does anybody know that?

Why are we using doorbells to update WPTRs instead of writing to the 
registers directly? I was assuming that using doorbells for the IH CAM 
had similar reasons. I think register writes can be problematic with 
certain power saving modes and virtualization. I'm not sure if there is 
a difference in terms of CPU overhead between writing a doorbell or 
writing an MMIO register.

If doorbells aren't working, it's probably some configuration issue. I'd 
rather fix those issues than throw away use of doorbells altogether.

Regards,
   Felix


>
> Thanks,
> Christian.
>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/ih_v6_0.c | 8 +++++++-
>>   1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/ih_v6_0.c b/drivers/gpu/drm/amd/amdgpu/ih_v6_0.c
>> index 65e5d21753f9..a97c85b0cb99 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/ih_v6_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/ih_v6_0.c
>> @@ -307,6 +307,11 @@ static int ih_v6_0_enable_ring(struct amdgpu_device *adev,
>>   	return 0;
>>   }
>>   
>> +static void ih_v6_0_retry_cam_ack(struct amdgpu_device *adev, u32 cam_index)
>> +{
>> +	WREG32_SOC15(OSSSYS, 0, regIH_RETRY_CAM_ACK, cam_index);
>> +}
>> +
>>   /**
>>    * ih_v6_0_irq_init - init and enable the interrupt ring
>>    *
>> @@ -807,7 +812,8 @@ static const struct amdgpu_ih_funcs ih_v6_0_funcs = {
>>   	.get_wptr = ih_v6_0_get_wptr,
>>   	.decode_iv = amdgpu_ih_decode_iv_helper,
>>   	.decode_iv_ts = amdgpu_ih_decode_iv_ts_helper,
>> -	.set_rptr = ih_v6_0_set_rptr
>> +	.set_rptr = ih_v6_0_set_rptr,
>> +	.retry_cam_ack = ih_v6_0_retry_cam_ack,
>>   };
>>   
>>   static void ih_v6_0_set_interrupt_funcs(struct amdgpu_device *adev)