Re: [PATCH 1/1] drm/amdkfd: Fix unaligned doorbell absolute offset for gfx8

[Shashank Sharma]

On 27/09/2023 19:27, Felix Kuehling wrote:
> [+Mukul]
>
> On 2023-09-27 12:16, Arvind Yadav wrote:
> > This patch is to adjust the absolute doorbell offset
> > against the doorbell id considering the doorbell
> > size of 32/64 bit.
> >
> > Cc: Christian Koenig<christian.koenig@xxxxxxx>
> > Cc: Alex Deucher<alexander.deucher@xxxxxxx>
> > Signed-off-by: Shashank Sharma<shashank.sharma@xxxxxxx>
> > Signed-off-by: Arvind Yadav<Arvind.Yadav@xxxxxxx>
> > ---
> >   drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c b/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c
> > index 0d3d538b64eb..c327f7f604d7 100644
> > --- a/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c
> > +++ b/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c
> > @@ -407,7 +407,16 @@ static int allocate_doorbell(struct qcm_process_device *qpd,
> >   
> >   	q->properties.doorbell_off = amdgpu_doorbell_index_on_bar(dev->adev,
> >   								  qpd->proc_doorbells,
> > -								  q->doorbell_id);
> > +								  0);
>
> Looks like we're now always calling amdgpu_doorbell_index_on_bar with 
> the third parameter = 0. So we could remove that parameter. It doesn't 
> do us any good and only causes bugs if we use any non-0 value.
Hey Felix,

Actually this was happening because in usermode KFD library the 
doorbell-size is for non-SOC15() hardware is hard coded to 4 bytes.

We added this fix just so that the library code doesn't need to be 
changed, but can still get aligned to kernel code.

GFX Usermode queue code uses this doorbell-index parameter, and it gives 
us the right offset.


Regards

Shashank

> > +
> > +	/* Adjust the absolute doorbell offset against the doorbell id considering
> > +	 * the doorbell size of 32/64 bit.
> > +	 */
> > +	if (!KFD_IS_SOC15(dev))
> > +		q->properties.doorbell_off += q->doorbell_id;
> > +	else
> > +		q->properties.doorbell_off += q->doorbell_id * 2;
>
> This could be simplified and generalized as
>
> 	q->properties.doorbell_off += q->doorbell_id * dev->kfd->device_info.doorbell_size / 4;

Agree, we can do this simplification.

- Shashank

> Regards,
>   Felix
>
>
> > +
> >   	return 0;
> >   }
> >