Re: [PATCH v9 01/32] drm: prime: add common helper to check scatterlist contiguity

Robin Murphy
2020-09-01T17:25:18Z

On 2020-08-26 07:32, Marek Szyprowski wrote:
> It is a common operation done by DRM drivers to check the contiguity
> of the DMA-mapped buffer described by a scatterlist in the
> sg_table object. Let's add a common helper for this operation.

I still think this could be hoisted even further out to the common
sgtable API level, but let's get the individual subsystems straightened
out first then worry about consolidation later.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
> ---
> drivers/gpu/drm/drm_gem_cma_helper.c | 23 +++------------------
> drivers/gpu/drm/drm_prime.c | 31 ++++++++++++++++++++++++++++
> include/drm/drm_prime.h | 2 ++
> 3 files changed, 36 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 822edeadbab3..59b9ca207b42 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -471,26 +471,9 @@ drm_gem_cma_prime_import_sg_table(struct drm_device *dev,
> {
> struct drm_gem_cma_object *cma_obj;
>
> - if (sgt->nents != 1) {
> - /* check if the entries in the sg_table are contiguous */
> - dma_addr_t next_addr = sg_dma_address(sgt->sgl);
> - struct scatterlist *s;
> - unsigned int i;
> -
> - for_each_sg(sgt->sgl, s, sgt->nents, i) {
> - /*
> - * sg_dma_address(s) is only valid for entries
> - * that have sg_dma_len(s) != 0
> - */
> - if (!sg_dma_len(s))
> - continue;
> -
> - if (sg_dma_address(s) != next_addr)
> - return ERR_PTR(-EINVAL);
> -
> - next_addr = sg_dma_address(s) + sg_dma_len(s);
> - }
> - }
> + /* check if the entries in the sg_table are contiguous */
> + if (drm_prime_get_contiguous_size(sgt) < attach->dmabuf->size)
> + return ERR_PTR(-EINVAL);
>
> /* Create a CMA GEM buffer. */
> cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size);
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 1693aa7c14b5..4ed5ed1f078c 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -825,6 +825,37 @@ struct sg_table *drm_prime_pages_to_sg(struct page **pages, unsigned int nr_page
> }
> EXPORT_SYMBOL(drm_prime_pages_to_sg);
>
> +/**
> + * drm_prime_get_contiguous_size - returns the contiguous size of the buffer
> + * @sgt: sg_table describing the buffer to check
> + *
> + * This helper calculates the contiguous size in the DMA address space
> + * of the the buffer described by the provided sg_table.
> + *
> + * This is useful for implementing
> + * &drm_gem_object_funcs.gem_prime_import_sg_table.
> + */
> +unsigned long drm_prime_get_contiguous_size(struct sg_table *sgt)
> +{
> + dma_addr_t expected = sg_dma_address(sgt->sgl);
> + struct scatterlist *sg;
> + unsigned long size = 0;
> + int i;
> +
> + for_each_sgtable_dma_sg(sgt, sg, i) {
> + unsigned int len = sg_dma_len(sg);
> +
> + if (!len)
> + break;
> + if (sg_dma_address(sg) != expected)
> + break;
> + expected += len;
> + size += len;
> + }
> + return size;
> +}
> +EXPORT_SYMBOL(drm_prime_get_contiguous_size);
> +
> /**
> * drm_gem_prime_export - helper library implementation of the export callback
> * @obj: GEM object to export
> diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
> index 9af7422b44cf..47ef11614627 100644
> --- a/include/drm/drm_prime.h
> +++ b/include/drm/drm_prime.h
> @@ -92,6 +92,8 @@ struct sg_table *drm_prime_pages_to_sg(struct page **pages, unsigned int nr_page
> struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
> int flags);
>
> +unsigned long drm_prime_get_contiguous_size(struct sg_table *sgt);
> +
> /* helper functions for importing */
> struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
> struct dma_buf *dma_buf,
>