Re: [PATCH 3/3] drm/panthor: Relax the check on the tiler chunk size
On Thu, 25 Apr 2024 10:28:56 +0100
Steven Price wrote:
> 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
>
> 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.
Ah, I got that wrong because v9 has this must-be-a-power-of-two
constraint (which is also where the erroneous 256k:2M range came from
BTW).
Chris, I guess you'd prefer to have the power-of-two constraint relaxed
too, so we can fine-tune the chunk size.
>
> 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.
Sure, I'll restrict the range to 128k:8M as you suggest.
Re: [PATCH 3/3] drm/panthor: Relax the check on the tiler chunk size
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
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(>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;
>
> /**
[PATCH 3/3] drm/panthor: Relax the check on the tiler chunk size
The field used to store the chunk size if 12 bits wide, and the encoding
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
---
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(>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;
/**
--
2.44.0
