[PATCH] drm/amdkfd: fix the wrong no space return while acquires packet buffer

[Huang Rui]

On Thu, Mar 19, 2020 at 07:42:04PM +0800, Pan, Xinhui wrote:
> 
> 
> > 2020年3月19日 18:51，Huang Rui <ray.huang at amd.com> 写道：
> > 
> > The queue buffer index starts from position 0, so the available buffer size
> > which starts from position 0 to rptr should be "rptr" index value. While the
> > packet_size_in_dwords == rptr, the available buffer is just good enough.
> > 
> > Signed-off-by: Huang Rui <ray.huang at amd.com>
> > ---
> > drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c b/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
> > index bae7064..4667c8f 100644
> > --- a/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
> > +++ b/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
> > @@ -263,7 +263,7 @@ int kq_acquire_packet_buffer(struct kernel_queue *kq,
> > 		/* make sure after rolling back to position 0, there is
> > 		 * still enough space.
> > 		 */
> > -		if (packet_size_in_dwords >= rptr)
> > +		if (packet_size_in_dwords > rptr)
> 
> rptr should always be > wptr unless ring is empty.
> 
> say, rptr is 4, packet_size_in_dwords is 4. Then wptr changes from 0 to 4, that is illegal.
> 

Hey, xinhui, yes. :-)

See the comment "we can only use up to queue_size_dword - 1 dwords", that
we cannot use the whole packet slots in the queue, it's to differentiate
empty and full cases.

Thanks,
Ray

> 
> > 			goto err_no_space;
> > 
> > 		/* fill nops, roll back and start at position 0 */
> > -- 
> > 2.7.4
> > 
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