On 2020-06-18 16:39, 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@xxxxxxxxxxx>
---
drivers/gpu/drm/drm_gem_cma_helper.c | 23 +++--------------------
drivers/gpu/drm/drm_prime.c | 26 ++++++++++++++++++++++++++
include/drm/drm_prime.h | 2 ++
3 files changed, 31 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..0784969894c1 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -825,6 +825,32 @@ 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 sg_dma_page_iter dma_iter;
+ unsigned long size = 0;
+
+ for_each_sgtable_dma_page(sgt, &dma_iter, 0) {
+ if (sg_page_iter_dma_address(&dma_iter) != expected)
+ break;
+ expected += PAGE_SIZE;
+ size += PAGE_SIZE;
Hmm, in many cases this is likely to be far less efficient than simply
using for_each_sgtable_dma() and sg_dma_len() equivalent to the original
implementation, and there doesn't seem to be any good reason for that.
Plus AFAICS it could potentially let false-positives through if someone
were to pass in a table with non-page-aligned lengths (I assume that's
expected never to happen, but still...)
Robin.
+ }
+ 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,
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