Messages in this thread Patch in this message | | | From | Alexandru Ardelean <> | Subject | [PATCH] lib/scatterlist: introduce sg_nents_for_dma() helper | Date | Wed, 27 Feb 2019 10:50:50 +0200 |
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From: Andy Shevchenko <andy.shevchenko@gmail.com>
Sometimes the user needs to split each entry on the mapped scatter list due to DMA length constrains. This helper returns a number of entities assuming that each of them is not bigger than supplied maximum length.
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com> ---
Patch was sent in 2016 initially to the DMA engine sub-system. Link: https://patchwork.kernel.org/patch/9389821/ This was part of a larger series: https://patchwork.kernel.org/project/linux-dmaengine/list/?q=sg_nents_for_dma&archive=both&series=&submitter=&delegate=&state=*
I'm not sure if this is supposed to go into DMAEngine or lib/scatterlist. It doesn't look like lib/scatterlist is managed by DMAEngine, so (by using the `get_maintainers.pl` script) I'm sending this patch to this group of parties.
Thanks Alex
include/linux/scatterlist.h | 1 + lib/scatterlist.c | 26 ++++++++++++++++++++++++++ 2 files changed, 27 insertions(+)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index b96f0d0b5b8f..4f40455c40e2 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -253,6 +253,7 @@ static inline void sg_init_marker(struct scatterlist *sgl, int sg_nents(struct scatterlist *sg); int sg_nents_for_len(struct scatterlist *sg, u64 len); +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len); struct scatterlist *sg_next(struct scatterlist *); struct scatterlist *sg_last(struct scatterlist *s, unsigned int); void sg_init_table(struct scatterlist *, unsigned int); diff --git a/lib/scatterlist.c b/lib/scatterlist.c index 9ba349e775ef..5a6fc32f485d 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -86,6 +86,32 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len) } EXPORT_SYMBOL(sg_nents_for_len); +/** + * sg_nents_for_dma - return count of DMA-capable entries in scatterlist + * @sgl: The scatterlist + * @sglen: The current number of entries + * @len: The maximum length of DMA-capable block + * + * Description: + * Determines the number of entries in @sgl which would be permitted in + * DMA-capable transfer if list had been split accordingly, taking into + * account chaining as well. + * + * Returns: + * the number of sgl entries needed + * + **/ +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len) +{ + struct scatterlist *sg; + int i, nents = 0; + + for_each_sg(sgl, sg, sglen, i) + nents += DIV_ROUND_UP(sg_dma_len(sg), len); + return nents; +} +EXPORT_SYMBOL(sg_nents_for_dma); + /** * sg_last - return the last scatterlist entry in a list * @sgl: First entry in the scatterlist -- 2.17.1
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