Re: [PATCH v3 1/9] drm/amdgpu: UAPI for user queue management

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 30.03.23 um 10:15 schrieb Shashank Sharma:
> Hello Pierre-Eric,
> [SNIP]
>> I'm also wondering why the doorbell needs a handle+offset but
>> other buffers are passed in as virtual addresses?
>>
> As you know, doorbell offset here will be an relative offset in this 
> doorbell page, but the MQD needs the absolute offset on the doorbell 
> PCI BAR.
>
> So kernel needs both the object as well as relative offset to 
> calculate absolute offset.
>
> something like: absolute offset = base offset of this doorbell page + 
> relative offset of this doorbell.

Another much more obvious reason is that the doorbell doesn't have a 
virtual address.

At least for GFX the doorbell is used to signal to the hw that new 
commands are available. So as long as we don't want a shader to kick of 
other work we don't need to map the doorbell into the GPUVM address space.

Christian.