From: Thierry Reding treding@nvidia.com
Add a few helpers to count the number of contiguous DMA chunks found in an SG table. This is useful to determine whether or not a mapping can be used by drivers whose devices need contiguous memory.
Signed-off-by: Thierry Reding treding@nvidia.com --- include/linux/scatterlist.h | 11 +++++++++++ lib/scatterlist.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 6eec50fb36c8..51a8416623a9 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -262,6 +262,7 @@ int sg_split(struct scatterlist *in, const int in_mapped_nents, const size_t *split_sizes, struct scatterlist **out, int *out_mapped_nents, gfp_t gfp_mask); +unsigned int sg_dma_count_chunks(struct scatterlist *sgl, unsigned int nents);
typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t); typedef void (sg_free_fn)(struct scatterlist *, unsigned int); @@ -306,6 +307,16 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents, size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents, size_t buflen, off_t skip);
+static inline unsigned int sgt_dma_count_chunks(struct sg_table *sgt) +{ + return sg_dma_count_chunks(sgt->sgl, sgt->nents); +} + +static inline bool sgt_dma_contiguous(struct sg_table *sgt) +{ + return sgt_dma_count_chunks(sgt) == 1; +} + /* * Maximum number of entries that will be allocated in one piece, if * a list larger than this is required then chaining will be utilized. diff --git a/lib/scatterlist.c b/lib/scatterlist.c index c2cf2c311b7d..4c0d11968f8d 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -142,6 +142,35 @@ void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen) } EXPORT_SYMBOL(sg_init_one);
+/** + * sg_dma_count_chunks - return number of contiguous DMA chunks in scatterlist + * @sgl: SG table + * @nents: number of entries in SG table + */ +unsigned int sg_dma_count_chunks(struct scatterlist *sgl, unsigned int nents) +{ + dma_addr_t next = ~(dma_addr_t)0; + unsigned int count = 0, i; + struct scatterlist *s; + + for_each_sg(sgl, s, 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) { + next = sg_dma_address(s) + sg_dma_len(s); + count++; + } + } + + return count; +} +EXPORT_SYMBOL(sg_dma_count_chunks); + /* * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree * helpers.