Re: [PATCH v3 3/5] drm/panthor: Relax the constraints on the tiler chunk size

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 2 May 2024 16:47:56 +0100
Steven Price <steven.price@arm.com> wrote:

> On 02/05/2024 16:40, Boris Brezillon wrote:
> > 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, and all known implementations seem to
> > impose a [128k:8M] range, so do the same here.
> > 
> > We also relax the power-of-two constraint, which doesn't seem to
> > exist on v10. This will allow userspace to fine-tune initial/max
> > tiler memory on memory-constrained devices.
> > 
> > v3:
> > - Add R-bs
> > - Fix valid range in the kerneldoc  
> 
> Sadly the fixed range didn't make it to this posting... ;)

My bad, I was checking the uAPI header and thought I had already fixed
it the other day. Should be good in v4.

> 
> Steve
> 
> > 
> > v2:
> > - Turn the power-of-two constraint into a page-aligned constraint to allow
> >   fine-tune of the initial/max heap memory size
> > - Fix the panthor_heap_create() kerneldoc
> > 
> > Fixes: 9cca48fa4f89 ("drm/panthor: Add the heap logical block")
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
> > Reviewed-by: Steven Price <steven.price@arm.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_heap.c | 8 ++++----
> >  include/uapi/drm/panthor_drm.h         | 6 +++++-
> >  2 files changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/panthor/panthor_heap.c b/drivers/gpu/drm/panthor/panthor_heap.c
> > index 3be86ec383d6..683bb94761bc 100644
> > --- a/drivers/gpu/drm/panthor/panthor_heap.c
> > +++ b/drivers/gpu/drm/panthor/panthor_heap.c
> > @@ -253,8 +253,8 @@ int panthor_heap_destroy(struct panthor_heap_pool *pool, u32 handle)
> >   * @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.
> > + * @chunk_size: The size of each chunk. Must be page-aligned and lie in the
> > + * [128k:2M] range.
> >   * @max_chunks: Maximum number of chunks that can be allocated.
> >   * @target_in_flight: Maximum number of in-flight render passes.
> >   * @heap_ctx_gpu_va: Pointer holding the GPU address of the allocated heap
> > @@ -284,8 +284,8 @@ int panthor_heap_create(struct panthor_heap_pool *pool,
> >  	if (initial_chunk_count > max_chunks)
> >  		return -EINVAL;
> >  
> > -	if (hweight32(chunk_size) != 1 ||
> > -	    chunk_size < SZ_256K || chunk_size > SZ_2M)
> > +	if (!IS_ALIGNED(chunk_size, PAGE_SIZE) ||
> > +	    chunk_size < SZ_128K || 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..b8220d2e698f 100644
> > --- a/include/uapi/drm/panthor_drm.h
> > +++ b/include/uapi/drm/panthor_drm.h
> > @@ -898,7 +898,11 @@ 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 page-aligned and lie in the [128k:8M] range.
> > +	 */
> >  	__u32 chunk_size;
> >  
> >  	/**  
>