On Tue, 18 Feb 2025 23:25:36 +0000
Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx> wrote:
> Panfrost heap BOs grow on demand when the GPU triggers a page fault after
> accessing an address within the BO's virtual range.
>
> We still store the sgts we get back from the shmem sparse allocation function,
> since it was decided management of sparse memory SGTs should be done by client
> drivers rather than the shmem subsystem.
>
> Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/panfrost/panfrost_gem.c | 12 ++--
> drivers/gpu/drm/panfrost/panfrost_gem.h | 2 +-
> drivers/gpu/drm/panfrost/panfrost_mmu.c | 85 +++++--------------------
> 3 files changed, 25 insertions(+), 74 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 8e0ff3efede7..0cda2c4e524f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -40,10 +40,10 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)
> int n_sgt = bo->base.base.size / SZ_2M;
>
> for (i = 0; i < n_sgt; i++) {
> - if (bo->sgts[i].sgl) {
> - dma_unmap_sgtable(pfdev->dev, &bo->sgts[i],
> + if (bo->sgts[i]) {
> + dma_unmap_sgtable(pfdev->dev, bo->sgts[i],
> DMA_BIDIRECTIONAL, 0);
> - sg_free_table(&bo->sgts[i]);
> + sg_free_table(bo->sgts[i]);
> }
> }
> kvfree(bo->sgts);
> @@ -274,7 +274,11 @@ panfrost_gem_create(struct drm_device *dev, size_t size, u32 flags)
> if (flags & PANFROST_BO_HEAP)
> size = roundup(size, SZ_2M);
>
> - shmem = drm_gem_shmem_create(dev, size);
> + if (flags & PANFROST_BO_HEAP)
> + shmem = drm_gem_shmem_create_sparse(dev, size);
> + else
> + shmem = drm_gem_shmem_create(dev, size);
> +
> if (IS_ERR(shmem))
> return ERR_CAST(shmem);
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index 7516b7ecf7fe..2a8d0752011e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -11,7 +11,7 @@ struct panfrost_mmu;
>
> struct panfrost_gem_object {
> struct drm_gem_shmem_object base;
> - struct sg_table *sgts;
> + struct sg_table **sgts;
I guess using an xarray here would make sense. Or maybe even an
sg_append_table, since we don't expect holes in the populated pages.
This makes me wonder if we really want the gem_shmem layer to automate
sgt creation for sparse GEM objects. Looks like something the driver
can easily optimize for its use-case.
