Commit 80c70bfb authored by Andy Shevchenko's avatar Andy Shevchenko Committed by Vinod Koul
Browse files

scatterlist: introduce sg_nents_for_dma() helper 



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.

Reviewed-by: default avatarBjorn Andersson <andersson@kernel.org>
Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20260108105619.3513561-2-andriy.shevchenko@linux.intel.com


Signed-off-by: default avatarVinod Koul <vkoul@kernel.org>
parent fe7b87d9

include/linux/scatterlist.h

+2 −0
Original line number Diff line number Diff line
@@ -441,6 +441,8 @@ 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_last(struct scatterlist *s, unsigned int);

void sg_init_table(struct scatterlist *, unsigned int);

void sg_init_one(struct scatterlist *, const void *, unsigned int);

lib/scatterlist.c

+26 −0
Original line number Diff line number Diff line
@@ -64,6 +64,32 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len) 
}

EXPORT_SYMBOL(sg_nents_for_len);



/**

 * sg_nents_for_dma - return the 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