From a321e91b6d73ed011ffceed384c40d2785cf723b Mon Sep 17 00:00:00 2001 From: Imre Deak Date: Wed, 27 Feb 2013 17:02:56 -0800 Subject: lib/scatterlist: add simple page iterator Add an iterator to walk through a scatter list a page at a time starting at a specific page offset. As opposed to the mapping iterator this is meant to be small, performing well even in simple loops like collecting all pages on the scatterlist into an array or setting up an iommu table based on the pages' DMA address. Signed-off-by: Imre Deak Cc: Maxim Levitsky Cc: Tejun Heo Cc: Daniel Vetter Tested-by: Stephen Warren Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/scatterlist.h | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) (limited to 'include/linux/scatterlist.h') diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 4bd6c06eb28e..788a853aa7a7 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -231,6 +231,41 @@ size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents, */ #define SG_MAX_SINGLE_ALLOC (PAGE_SIZE / sizeof(struct scatterlist)) +/* + * sg page iterator + * + * Iterates over sg entries page-by-page. On each successful iteration, + * @piter->page points to the current page, @piter->sg to the sg holding this + * page and @piter->sg_pgoffset to the page's page offset within the sg. The + * iteration will stop either when a maximum number of sg entries was reached + * or a terminating sg (sg_last(sg) == true) was reached. + */ +struct sg_page_iter { + struct page *page; /* current page */ + struct scatterlist *sg; /* sg holding the page */ + unsigned int sg_pgoffset; /* page offset within the sg */ + + /* these are internal states, keep away */ + unsigned int __nents; /* remaining sg entries */ + int __pg_advance; /* nr pages to advance at the + * next step */ +}; + +bool __sg_page_iter_next(struct sg_page_iter *piter); +void __sg_page_iter_start(struct sg_page_iter *piter, + struct scatterlist *sglist, unsigned int nents, + unsigned long pgoffset); + +/** + * for_each_sg_page - iterate over the pages of the given sg list + * @sglist: sglist to iterate over + * @piter: page iterator to hold current page, sg, sg_pgoffset + * @nents: maximum number of sg entries to iterate over + * @pgoffset: starting page offset + */ +#define for_each_sg_page(sglist, piter, nents, pgoffset) \ + for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \ + __sg_page_iter_next(piter);) /* * Mapping sg iterator -- cgit v1.2.3 From 4225fc8555a992c7f91d174ef424384d6781e144 Mon Sep 17 00:00:00 2001 From: Imre Deak Date: Wed, 27 Feb 2013 17:02:57 -0800 Subject: lib/scatterlist: use page iterator in the mapping iterator For better code reuse use the newly added page iterator to iterate through the pages. The offset, length within the page is still calculated by the mapping iterator as well as the actual mapping. Idea from Tejun Heo. Signed-off-by: Imre Deak Cc: Maxim Levitsky Cc: Tejun Heo Cc: Daniel Vetter Cc: James Hogan Cc: Stephen Warren Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/mmc/host/dw_mmc.c | 4 ++-- include/linux/scatterlist.h | 6 +++--- lib/scatterlist.c | 48 ++++++++++++++++++++++----------------------- 3 files changed, 28 insertions(+), 30 deletions(-) (limited to 'include/linux/scatterlist.h') diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c index 60063ccb4c4b..98342213ed21 100644 --- a/drivers/mmc/host/dw_mmc.c +++ b/drivers/mmc/host/dw_mmc.c @@ -1453,7 +1453,7 @@ static void dw_mci_read_data_pio(struct dw_mci *host) if (!sg_miter_next(sg_miter)) goto done; - host->sg = sg_miter->__sg; + host->sg = sg_miter->piter.sg; buf = sg_miter->addr; remain = sg_miter->length; offset = 0; @@ -1508,7 +1508,7 @@ static void dw_mci_write_data_pio(struct dw_mci *host) if (!sg_miter_next(sg_miter)) goto done; - host->sg = sg_miter->__sg; + host->sg = sg_miter->piter.sg; buf = sg_miter->addr; remain = sg_miter->length; offset = 0; diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 788a853aa7a7..2d8bdaef9611 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -293,11 +293,11 @@ struct sg_mapping_iter { void *addr; /* pointer to the mapped area */ size_t length; /* length of the mapped area */ size_t consumed; /* number of consumed bytes */ + struct sg_page_iter piter; /* page iterator */ /* these are internal states, keep away */ - struct scatterlist *__sg; /* current entry */ - unsigned int __nents; /* nr of remaining entries */ - unsigned int __offset; /* offset within sg */ + unsigned int __offset; /* offset within page */ + unsigned int __remaining; /* remaining bytes on page */ unsigned int __flags; }; diff --git a/lib/scatterlist.c b/lib/scatterlist.c index a1d15647d7db..b83c144d731f 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -449,9 +449,7 @@ void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl, { memset(miter, 0, sizeof(struct sg_mapping_iter)); - miter->__sg = sgl; - miter->__nents = nents; - miter->__offset = 0; + __sg_page_iter_start(&miter->piter, sgl, nents, 0); WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG))); miter->__flags = flags; } @@ -476,36 +474,35 @@ EXPORT_SYMBOL(sg_miter_start); */ bool sg_miter_next(struct sg_mapping_iter *miter) { - unsigned int off, len; - - /* check for end and drop resources from the last iteration */ - if (!miter->__nents) - return false; - sg_miter_stop(miter); - /* get to the next sg if necessary. __offset is adjusted by stop */ - while (miter->__offset == miter->__sg->length) { - if (--miter->__nents) { - miter->__sg = sg_next(miter->__sg); - miter->__offset = 0; - } else + /* + * Get to the next page if necessary. + * __remaining, __offset is adjusted by sg_miter_stop + */ + if (!miter->__remaining) { + struct scatterlist *sg; + unsigned long pgoffset; + + if (!__sg_page_iter_next(&miter->piter)) return false; - } - /* map the next page */ - off = miter->__sg->offset + miter->__offset; - len = miter->__sg->length - miter->__offset; + sg = miter->piter.sg; + pgoffset = miter->piter.sg_pgoffset; - miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT); - off &= ~PAGE_MASK; - miter->length = min_t(unsigned int, len, PAGE_SIZE - off); - miter->consumed = miter->length; + miter->__offset = pgoffset ? 0 : sg->offset; + miter->__remaining = sg->offset + sg->length - + (pgoffset << PAGE_SHIFT) - miter->__offset; + miter->__remaining = min_t(unsigned long, miter->__remaining, + PAGE_SIZE - miter->__offset); + } + miter->page = miter->piter.page; + miter->consumed = miter->length = miter->__remaining; if (miter->__flags & SG_MITER_ATOMIC) - miter->addr = kmap_atomic(miter->page) + off; + miter->addr = kmap_atomic(miter->page) + miter->__offset; else - miter->addr = kmap(miter->page) + off; + miter->addr = kmap(miter->page) + miter->__offset; return true; } @@ -532,6 +529,7 @@ void sg_miter_stop(struct sg_mapping_iter *miter) /* drop resources from the last iteration */ if (miter->addr) { miter->__offset += miter->consumed; + miter->__remaining -= miter->consumed; if (miter->__flags & SG_MITER_TO_SG) flush_kernel_dcache_page(miter->page); -- cgit v1.2.3