On 13/11/2025 10:39, Boris Brezillon wrote: > The meat in lock_region() is about packing a region range into a > single u64. The rest is just a regular reg write plus a > as_send_cmd_and_wait() call that can easily be inlined in > mmu_hw_do_operation_locked(). > > v2: > - New patch > > Signed-off-by: Boris Brezillon <[email protected]> > --- > drivers/gpu/drm/panthor/panthor_mmu.c | 14 +++++--------- > 1 file changed, 5 insertions(+), 9 deletions(-) > > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c > b/drivers/gpu/drm/panthor/panthor_mmu.c > index 186048fc2c25..f109c1588186 100644 > --- a/drivers/gpu/drm/panthor/panthor_mmu.c > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c > @@ -538,11 +538,9 @@ static int as_send_cmd_and_wait(struct panthor_device > *ptdev, u32 as_nr, u32 cmd > return status; > } > > -static int lock_region(struct panthor_device *ptdev, u32 as_nr, > - u64 region_start, u64 size) > +static u64 pack_region_range(u64 region_start, u64 size) > { > u8 region_width; > - u64 region; > u64 region_end = region_start + size; > > if (!size) Extra context: > return 0; Rather than skipping the lock for size==0 you are now performing a lock with LOCKADDR=0. The best documentation I can find for that says (for LOCKADDR_SIZE in the Midgard architecture): "Values in the range 0 to 10 are undefined and should not be used".
I think later versions upped the minimum to 14 (log2(1<<15)-1) for reasons due to supporting larger page sizes. While I suspect this might work (since we don't actually need a lock region when size==0) I don't think we should be relying on undefined behaviour. I think the simple solution is to move the size==0 check up into the caller. Thanks, Steve > @@ -565,11 +563,7 @@ static int lock_region(struct panthor_device *ptdev, u32 > as_nr, > */ > region_start &= GENMASK_ULL(63, region_width); > > - region = region_width | region_start; > - > - /* Lock the region that needs to be updated */ > - gpu_write64(ptdev, AS_LOCKADDR(as_nr), region); > - return as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_LOCK); > + return region_width | region_start; > } > > static int mmu_hw_do_operation_locked(struct panthor_device *ptdev, int > as_nr, > @@ -602,7 +596,9 @@ static int mmu_hw_do_operation_locked(struct > panthor_device *ptdev, int as_nr, > * power it up > */ > > - ret = lock_region(ptdev, as_nr, iova, size); > + /* Lock the region that needs to be updated */ > + gpu_write64(ptdev, AS_LOCKADDR(as_nr), pack_region_range(iova, size)); > + ret = as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_LOCK); > if (ret) > return ret; >
