On 25/04/2024 08:18, Boris Brezillon wrote:
> The field used to store the chunk size if 12 bits wide, and the encoding
NIT: ^^ is
> is chunk_size = chunk_header.chunk_size << 12, which gives us a
> theoretical [4k:8M] range. This range is further limited by
> implementation constraints, but those shouldn't be enforced kernel side.
>
> Fixes: 9cca48fa4f89 ("drm/panthor: Add the heap logical block")
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
There's also a kerneldoc comment above panthor_heap_create that needs
updating too:
> /**
> * panthor_heap_create() - Create a heap context
> * @pool: Pool to instantiate the heap context from.
> * @initial_chunk_count: Number of chunk allocated at initialization time.
> * Must be at least 1.
> * @chunk_size: The size of each chunk. Must be a power of two between 256k
> * and 2M.
I'm also a little unsure on whether this is the right change. The
"implementation defined" min/max in the hardware docs say 128KiB to
8MiB. I'm not convinced it makes sense to increase the range beyond that.
As far as I'm aware the "must be a power of 2" isn't actually a
requirement (it's certainly not a requirement of the storage format) so
the kernel is already being more restrictive than necessary.
It seems like a good idea to keep the uAPI requirements stricter than
necessary and relax them in the future if we have a good reason (e.g.
new hardware supports a wider range). But matching the existing hardware
range of 128KB-8MB would obviously make sense now.
Steve
> ---
> drivers/gpu/drm/panthor/panthor_heap.c | 2 +-
> include/uapi/drm/panthor_drm.h | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_heap.c b/drivers/gpu/drm/panthor/panthor_heap.c
> index 8728c9bb76e4..146ea2f57764 100644
> --- a/drivers/gpu/drm/panthor/panthor_heap.c
> +++ b/drivers/gpu/drm/panthor/panthor_heap.c
> @@ -285,7 +285,7 @@ int panthor_heap_create(struct panthor_heap_pool *pool,
> return -EINVAL;
>
> if (hweight32(chunk_size) != 1 ||
> - chunk_size < SZ_256K || chunk_size > SZ_2M)
> + chunk_size < SZ_4K || chunk_size > SZ_8M)
> return -EINVAL;
>
> down_read(&pool->lock);
> diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
> index 5db80a0682d5..80c0716361b9 100644
> --- a/include/uapi/drm/panthor_drm.h
> +++ b/include/uapi/drm/panthor_drm.h
> @@ -898,7 +898,7 @@ struct drm_panthor_tiler_heap_create {
> /** @initial_chunk_count: Initial number of chunks to allocate. Must be at least one. */
> __u32 initial_chunk_count;
>
> - /** @chunk_size: Chunk size. Must be a power of two at least 256KB large. */
> + /** @chunk_size: Chunk size. Must be a power of two and lie in the [4k:8M] range. */
> __u32 chunk_size;
>
> /**
