On Thu, Oct 2, 2025 at 3:41 AM Steven Price <steven.pr...@arm.com> wrote:
>
> On 16/09/2025 22:08, Chia-I Wu wrote:
> > No need to call mmu_hw_wait_ready after panthor_gpu_flush_caches or
> > before returning from mmu_hw_flush_caches.
>
> Why is there no need? If we attempt to send a command when the hardware
> is busy then the command will be dropped (so the cache flush won't
> happen), and if we don't wait for the unlock command to complete then
> then we don't know that the flush is complete.
We have this sequence of calls
mmu_hw_wait_ready
panthor_gpu_flush_caches
mmu_hw_wait_ready
mmu_hw_cmd_unlock
mmu_hw_wait_ready
I could be utterly wrong, but my assumption was that
panthor_gpu_flush_caches does not cause AS_STATUS_AS_ACTIVE, at least
by the time it returns. That's why I removed the second wait.
We also always wait before issuing a cmd. Removing the last wait here
avoids double waits for panthor_mmu_as_{enable,disable}. It does leave
the cmd in flight when panthor_vm_flush_range returns, but whoever
issues a new cmd will wait on the flush.
>
> Thanks,
> Steve
>
> > Signed-off-by: Chia-I Wu <olva...@gmail.com>
> > ---
> > drivers/gpu/drm/panthor/panthor_mmu.c | 7 ++-----
> > 1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c
> > b/drivers/gpu/drm/panthor/panthor_mmu.c
> > index 373871aeea9f4..c223e3fadf92e 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -669,12 +669,9 @@ static int mmu_hw_flush_caches(struct panthor_device
> > *ptdev, int as_nr, u64 iova
> > * at the end of the GPU_CONTROL cache flush command, unlike
> > * AS_COMMAND_FLUSH_MEM or AS_COMMAND_FLUSH_PT.
> > */
> > - ret = mmu_hw_wait_ready(ptdev, as_nr);
> > - if (!ret)
> > - mmu_hw_cmd_unlock(ptdev, as_nr);
> > + mmu_hw_cmd_unlock(ptdev, as_nr);
> >
> > - /* Wait for the unlock command to complete */
> > - return mmu_hw_wait_ready(ptdev, as_nr);
> > + return 0;
> > }
> >
> > static int mmu_hw_do_operation(struct panthor_vm *vm,
>
