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    SubjectRe: [PATCH v7 01/36] drm: prime: add common helper to check scatterlist contiguity
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    On 19.06.2020 12:36, 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.
    >
    > Signed-off-by: Marek Szyprowski <m.szyprowski@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 06a5b9ee1fe0..41566a15dabd 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 bbfc713bfdc3..226cd6ad3985 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;


    I wander if in some dark corners of the kernel 0-length buffers can be
    in use :)


    > + 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);
    > +

    Reviewed-by <a.hajda@samsung.com>

    Regards
    Andrzej


    > /* helper functions for importing */
    > struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
    > struct dma_buf *dma_buf,

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