Re: [PATCH v2 08/12] drm/amdgpu: use doorbell manager for kfd kernel doorbells

[Shashank Sharma <shashank.sharma@amd.com>]

On 24/04/2023 21:56, Felix Kuehling wrote:
> On 2023-04-22 2:39, Shashank Sharma wrote:
>> - KFD process level doorbells: doorbell pages which are allocated by 
>> kernel but mapped and written by userspace processes, saved in struct 
>> pdd->qpd->doorbells
>>
>> size = kfd_doorbell_process_slice.
>>
>> We realized that we only need 1-2 doorbells for KFD kernel level 
>> stuff (so kept it one page), but need 2-page of doorbells for KFD 
>> process, so they are sized accordingly.
>>
>> We have also run kfd_test_suit and verified the changes for any 
>> regression. Hope this helps in explaining the design.
>
> Right, I missed that this was only for kernel doorbells. I wonder 
> whether KFD really needs its own page here. I think we only need a 
> doorbell for HWS. And when we use MES, I think even that isn't needed 
> because MES packet submissions go through amdgpu. So maybe KFD doesn't 
> need its own kernel-mode doorbell page any more on systems with user 
> graphics mode queues.

Yeah, for any IP with MES enabled, KFD doesn't need kernel level 
doorbells. But I still allocated a page just to make sure we do not 
break any non-MES platforms or use cases where MES is deliberately 
disabled from kernel command line. Hope that works for you.

- Shashank

>
> Regards,
>   Felix
>
>
>>
>> - Shashank