| Message ID | 1457435715-24740-5-git-send-email-boris.brezillon@free-electrons.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Boris, Thank you for the patch. On Tuesday 08 March 2016 12:15:12 Boris Brezillon wrote: > sg_alloc_table_from_buf() provides an easy solution to create an sg_table > from a virtual address pointer. This function takes care of dealing with > vmallocated buffers, buffer alignment, or DMA engine limitations (maximum > DMA transfer size). > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > --- > include/linux/scatterlist.h | 24 ++++++++ > lib/scatterlist.c | 142 +++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 166 insertions(+) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 556ec1e..4a75362 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -41,6 +41,27 @@ struct sg_table { > unsigned int orig_nents; /* original size of list */ > }; > > +/** > + * struct sg_constraints - SG constraints structure > + * > + * @max_chunk_len: maximum chunk buffer length. Each SG entry has to be > smaller > + * than this value. Zero means no constraint. > + * @required_alignment: minimum alignment. Is used for both size and > pointer > + * alignment. If this constraint is not met, the function > + * should return -EINVAL. > + * @preferred_alignment: preferred alignment. Mainly used to optimize > + * throughput when the DMA engine performs better when > + * doing aligned accesses. > + * > + * This structure is here to help sg_alloc_table_from_buf() create the > optimal > + * SG list based on DMA engine constraints. > + */ > +struct sg_constraints { > + size_t max_chunk_len; > + size_t required_alignment; > + size_t preferred_alignment; > +}; > + > /* > * Notes on SG table design. > * > @@ -265,6 +286,9 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, > struct page **pages, unsigned int n_pages, > unsigned long offset, unsigned long size, > gfp_t gfp_mask); > +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t > len, > + const struct sg_constraints *constraints, > + gfp_t gfp_mask); > > size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void > *buf, size_t buflen, off_t skip, bool to_buffer); > diff --git a/lib/scatterlist.c b/lib/scatterlist.c > index bafa993..706b583 100644 > --- a/lib/scatterlist.c > +++ b/lib/scatterlist.c > @@ -433,6 +433,148 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, > } > EXPORT_SYMBOL(sg_alloc_table_from_pages); > > +static size_t sg_buf_chunk_len(const void *buf, size_t len, > + const struct sg_constraints *cons) > +{ > + size_t chunk_len = len; > + > + if (cons->max_chunk_len) > + chunk_len = min_t(size_t, chunk_len, cons->max_chunk_len); > + > + if (is_vmalloc_addr(buf)) > + chunk_len = min_t(size_t, chunk_len, > + PAGE_SIZE - offset_in_page(buf)); This will lead to page-sized scatter-gather entries even for pages of the vmalloc memory that happen to be physically contiguous. That works, but I wonder whether we'd want to be more efficient. > + if (!IS_ALIGNED((unsigned long)buf, cons->preferred_alignment)) { > + const void *aligned_buf = PTR_ALIGN(buf, > + cons->preferred_alignment); > + size_t unaligned_len = (unsigned long)(aligned_buf - buf); > + > + chunk_len = min_t(size_t, chunk_len, unaligned_len); > + } else if (chunk_len > cons->preferred_alignment) { > + chunk_len &= ~(cons->preferred_alignment - 1); > + } > + > + return chunk_len; > +} > + > +#define sg_for_each_chunk_in_buf(buf, len, chunk_len, constraints) \ > + for (chunk_len = sg_buf_chunk_len(buf, len, constraints); \ > + len; \ > + len -= chunk_len, buf += chunk_len, \ > + chunk_len = sg_buf_chunk_len(buf, len, constraints)) > + > +static int sg_check_constraints(struct sg_constraints *cons, > + const void *buf, size_t len) > +{ > + if (!cons->required_alignment) > + cons->required_alignment = 1; > + > + if (!cons->preferred_alignment) > + cons->preferred_alignment = cons->required_alignment; > + > + /* Test if buf and len are properly aligned. */ > + if (!IS_ALIGNED((unsigned long)buf, cons->required_alignment) || > + !IS_ALIGNED(len, cons->required_alignment)) > + return -EINVAL; > + > + /* > + * if the buffer has been vmallocated and required_alignment is > + * more than PAGE_SIZE we cannot guarantee it. > + */ > + if (is_vmalloc_addr(buf) && cons->required_alignment > PAGE_SIZE) > + return -EINVAL; > + > + /* > + * max_chunk_len has to be aligned to required_alignment to > + * guarantee that all buffer chunks are aligned correctly. > + */ > + if (!IS_ALIGNED(cons->max_chunk_len, cons->required_alignment)) > + return -EINVAL; > + > + /* > + * preferred_alignment has to be aligned to required_alignment > + * to avoid misalignment of buffer chunks. > + */ > + if (!IS_ALIGNED(cons->preferred_alignment, cons->required_alignment)) > + return -EINVAL; > + > + return 0; > +} > + > +/** > + * sg_alloc_table_from_buf - create an SG table from a buffer > + * > + * @sgt: SG table > + * @buf: buffer you want to create this SG table from > + * @len: length of buf > + * @constraints: optional constraints to take into account when creating > + * the SG table. Can be NULL if no specific constraints are > + * required. > + * @gfp_mask: type of allocation to use when creating the table > + * > + * This function creates an SG table from a buffer, its length and some > + * SG constraints. > + * > + * Note: This function supports vmallocated buffers. What other types of memory does it support ? kmalloc() quite obviously, are there others ? I think you should explicitly list the memory types that the function intends to support. > + */ > +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t > len, > + const struct sg_constraints *constraints, > + gfp_t gfp_mask) > +{ > + struct sg_constraints cons = { }; > + size_t remaining, chunk_len; > + const void *sg_buf; > + int i, ret; > + > + if (constraints) > + cons = *constraints; > + > + ret = sg_check_constraints(&cons, buf, len); > + if (ret) > + return ret; > + > + sg_buf = buf; > + remaining = len; > + i = 0; > + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) > + i++; > + > + ret = sg_alloc_table(sgt, i, gfp_mask); > + if (ret) > + return ret; > + > + sg_buf = buf; > + remaining = len; > + i = 0; > + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) { > + if (is_vmalloc_addr(sg_buf)) { > + struct page *vm_page; > + > + vm_page = vmalloc_to_page(sg_buf); > + if (!vm_page) { > + ret = -ENOMEM; > + goto err_free_table; > + } > + > + sg_set_page(&sgt->sgl[i], vm_page, chunk_len, > + offset_in_page(sg_buf)); > + } else { > + sg_set_buf(&sgt->sgl[i], sg_buf, chunk_len); > + } > + > + i++; > + } > + > + return 0; > + > +err_free_table: > + sg_free_table(sgt); > + > + return ret; > +} > +EXPORT_SYMBOL(sg_alloc_table_from_buf); > + > void __sg_page_iter_start(struct sg_page_iter *piter, > struct scatterlist *sglist, unsigned int nents, > unsigned long pgoffset)
Hi Laurent, On Tue, 08 Mar 2016 18:51:49 +0200 Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > Hi Boris, > > Thank you for the patch. > > On Tuesday 08 March 2016 12:15:12 Boris Brezillon wrote: > > sg_alloc_table_from_buf() provides an easy solution to create an sg_table > > from a virtual address pointer. This function takes care of dealing with > > vmallocated buffers, buffer alignment, or DMA engine limitations (maximum > > DMA transfer size). > > > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > > --- > > include/linux/scatterlist.h | 24 ++++++++ > > lib/scatterlist.c | 142 +++++++++++++++++++++++++++++++++++++++++ > > 2 files changed, 166 insertions(+) > > > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > > index 556ec1e..4a75362 100644 > > --- a/include/linux/scatterlist.h > > +++ b/include/linux/scatterlist.h > > @@ -41,6 +41,27 @@ struct sg_table { > > unsigned int orig_nents; /* original size of list */ > > }; > > > > +/** > > + * struct sg_constraints - SG constraints structure > > + * > > + * @max_chunk_len: maximum chunk buffer length. Each SG entry has to be > > smaller > > + * than this value. Zero means no constraint. > > + * @required_alignment: minimum alignment. Is used for both size and > > pointer > > + * alignment. If this constraint is not met, the function > > + * should return -EINVAL. > > + * @preferred_alignment: preferred alignment. Mainly used to optimize > > + * throughput when the DMA engine performs better when > > + * doing aligned accesses. > > + * > > + * This structure is here to help sg_alloc_table_from_buf() create the > > optimal > > + * SG list based on DMA engine constraints. > > + */ > > +struct sg_constraints { > > + size_t max_chunk_len; > > + size_t required_alignment; > > + size_t preferred_alignment; > > +}; > > + > > /* > > * Notes on SG table design. > > * > > @@ -265,6 +286,9 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, > > struct page **pages, unsigned int n_pages, > > unsigned long offset, unsigned long size, > > gfp_t gfp_mask); > > +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t > > len, > > + const struct sg_constraints *constraints, > > + gfp_t gfp_mask); > > > > size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void > > *buf, size_t buflen, off_t skip, bool to_buffer); > > diff --git a/lib/scatterlist.c b/lib/scatterlist.c > > index bafa993..706b583 100644 > > --- a/lib/scatterlist.c > > +++ b/lib/scatterlist.c > > @@ -433,6 +433,148 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, > > } > > EXPORT_SYMBOL(sg_alloc_table_from_pages); > > > > +static size_t sg_buf_chunk_len(const void *buf, size_t len, > > + const struct sg_constraints *cons) > > +{ > > + size_t chunk_len = len; > > + > > + if (cons->max_chunk_len) > > + chunk_len = min_t(size_t, chunk_len, cons->max_chunk_len); > > + > > + if (is_vmalloc_addr(buf)) > > + chunk_len = min_t(size_t, chunk_len, > > + PAGE_SIZE - offset_in_page(buf)); > > This will lead to page-sized scatter-gather entries even for pages of the > vmalloc memory that happen to be physically contiguous. That works, but I > wonder whether we'd want to be more efficient. Hm, I thought dma_map_sg() was taking care of merging p?ysically contiguous memory regions, but maybe I'm wrong. Anyway, that's definitely something I can add at this level. > > > + if (!IS_ALIGNED((unsigned long)buf, cons->preferred_alignment)) { > > + const void *aligned_buf = PTR_ALIGN(buf, > > + cons->preferred_alignment); > > + size_t unaligned_len = (unsigned long)(aligned_buf - buf); > > + > > + chunk_len = min_t(size_t, chunk_len, unaligned_len); > > + } else if (chunk_len > cons->preferred_alignment) { > > + chunk_len &= ~(cons->preferred_alignment - 1); > > + } > > + > > + return chunk_len; > > +} > > + > > +#define sg_for_each_chunk_in_buf(buf, len, chunk_len, constraints) \ > > + for (chunk_len = sg_buf_chunk_len(buf, len, constraints); \ > > + len; \ > > + len -= chunk_len, buf += chunk_len, \ > > + chunk_len = sg_buf_chunk_len(buf, len, constraints)) > > + > > +static int sg_check_constraints(struct sg_constraints *cons, > > + const void *buf, size_t len) > > +{ > > + if (!cons->required_alignment) > > + cons->required_alignment = 1; > > + > > + if (!cons->preferred_alignment) > > + cons->preferred_alignment = cons->required_alignment; > > + > > + /* Test if buf and len are properly aligned. */ > > + if (!IS_ALIGNED((unsigned long)buf, cons->required_alignment) || > > + !IS_ALIGNED(len, cons->required_alignment)) > > + return -EINVAL; > > + > > + /* > > + * if the buffer has been vmallocated and required_alignment is > > + * more than PAGE_SIZE we cannot guarantee it. > > + */ > > + if (is_vmalloc_addr(buf) && cons->required_alignment > PAGE_SIZE) > > + return -EINVAL; > > + > > + /* > > + * max_chunk_len has to be aligned to required_alignment to > > + * guarantee that all buffer chunks are aligned correctly. > > + */ > > + if (!IS_ALIGNED(cons->max_chunk_len, cons->required_alignment)) > > + return -EINVAL; > > + > > + /* > > + * preferred_alignment has to be aligned to required_alignment > > + * to avoid misalignment of buffer chunks. > > + */ > > + if (!IS_ALIGNED(cons->preferred_alignment, cons->required_alignment)) > > + return -EINVAL; > > + > > + return 0; > > +} > > + > > +/** > > + * sg_alloc_table_from_buf - create an SG table from a buffer > > + * > > + * @sgt: SG table > > + * @buf: buffer you want to create this SG table from > > + * @len: length of buf > > + * @constraints: optional constraints to take into account when creating > > + * the SG table. Can be NULL if no specific constraints are > > + * required. > > + * @gfp_mask: type of allocation to use when creating the table > > + * > > + * This function creates an SG table from a buffer, its length and some > > + * SG constraints. > > + * > > + * Note: This function supports vmallocated buffers. > > What other types of memory does it support ? kmalloc() quite obviously, are > there others ? I think you should explicitly list the memory types that the > function intends to support. Sure, I can explicitly list all memory types. Do you see any other kind of memory other than the vmalloced and physically-contiguous ones? Thanks for your review. Boris
On Tue, 8 Mar 2016 12:15:12 +0100 Boris Brezillon <boris.brezillon@free-electrons.com> wrote: > sg_alloc_table_from_buf() provides an easy solution to create an sg_table > from a virtual address pointer. This function takes care of dealing with > vmallocated buffers, buffer alignment, or DMA engine limitations (maximum > DMA transfer size). > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > --- > include/linux/scatterlist.h | 24 ++++++++ > lib/scatterlist.c | 142 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 166 insertions(+) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 556ec1e..4a75362 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -41,6 +41,27 @@ struct sg_table { > unsigned int orig_nents; /* original size of list */ > }; > > +/** > + * struct sg_constraints - SG constraints structure > + * > + * @max_chunk_len: maximum chunk buffer length. Each SG entry has to be smaller > + * than this value. Zero means no constraint. > + * @required_alignment: minimum alignment. Is used for both size and pointer > + * alignment. If this constraint is not met, the function > + * should return -EINVAL. > + * @preferred_alignment: preferred alignment. Mainly used to optimize > + * throughput when the DMA engine performs better when > + * doing aligned accesses. > + * > + * This structure is here to help sg_alloc_table_from_buf() create the optimal > + * SG list based on DMA engine constraints. > + */ > +struct sg_constraints { > + size_t max_chunk_len; > + size_t required_alignment; > + size_t preferred_alignment; > +}; > + Hm, we seem to have another case in NAND controller drivers. Some drivers do not support scattergather accesses and have to provide a single physically contiguous memory region to transfer the whole NAND page. Could we add a ->max_entries field to the sg_contraints struct to allow those drivers to use the generic mtd_map_buf() function, and fallback to a bounce buffer approach (or PIO access approach) when sg_alloc_table_from_buf() fails to fulfill this constraint. We could also define another 'non-sg' function to do the 'physically contiguous' check, but in any case, I'd like to avoid letting each driver code its own checking function. What do you think? > /* > * Notes on SG table design. > * > @@ -265,6 +286,9 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, > struct page **pages, unsigned int n_pages, > unsigned long offset, unsigned long size, > gfp_t gfp_mask); > +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t len, > + const struct sg_constraints *constraints, > + gfp_t gfp_mask); > > size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf, > size_t buflen, off_t skip, bool to_buffer); > diff --git a/lib/scatterlist.c b/lib/scatterlist.c > index bafa993..706b583 100644 > --- a/lib/scatterlist.c > +++ b/lib/scatterlist.c > @@ -433,6 +433,148 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, > } > EXPORT_SYMBOL(sg_alloc_table_from_pages); > > +static size_t sg_buf_chunk_len(const void *buf, size_t len, > + const struct sg_constraints *cons) > +{ > + size_t chunk_len = len; > + > + if (cons->max_chunk_len) > + chunk_len = min_t(size_t, chunk_len, cons->max_chunk_len); > + > + if (is_vmalloc_addr(buf)) > + chunk_len = min_t(size_t, chunk_len, > + PAGE_SIZE - offset_in_page(buf)); > + > + if (!IS_ALIGNED((unsigned long)buf, cons->preferred_alignment)) { > + const void *aligned_buf = PTR_ALIGN(buf, > + cons->preferred_alignment); > + size_t unaligned_len = (unsigned long)(aligned_buf - buf); > + > + chunk_len = min_t(size_t, chunk_len, unaligned_len); > + } else if (chunk_len > cons->preferred_alignment) { > + chunk_len &= ~(cons->preferred_alignment - 1); > + } > + > + return chunk_len; > +} > + > +#define sg_for_each_chunk_in_buf(buf, len, chunk_len, constraints) \ > + for (chunk_len = sg_buf_chunk_len(buf, len, constraints); \ > + len; \ > + len -= chunk_len, buf += chunk_len, \ > + chunk_len = sg_buf_chunk_len(buf, len, constraints)) > + > +static int sg_check_constraints(struct sg_constraints *cons, > + const void *buf, size_t len) > +{ > + if (!cons->required_alignment) > + cons->required_alignment = 1; > + > + if (!cons->preferred_alignment) > + cons->preferred_alignment = cons->required_alignment; > + > + /* Test if buf and len are properly aligned. */ > + if (!IS_ALIGNED((unsigned long)buf, cons->required_alignment) || > + !IS_ALIGNED(len, cons->required_alignment)) > + return -EINVAL; > + > + /* > + * if the buffer has been vmallocated and required_alignment is > + * more than PAGE_SIZE we cannot guarantee it. > + */ > + if (is_vmalloc_addr(buf) && cons->required_alignment > PAGE_SIZE) > + return -EINVAL; > + > + /* > + * max_chunk_len has to be aligned to required_alignment to > + * guarantee that all buffer chunks are aligned correctly. > + */ > + if (!IS_ALIGNED(cons->max_chunk_len, cons->required_alignment)) > + return -EINVAL; > + > + /* > + * preferred_alignment has to be aligned to required_alignment > + * to avoid misalignment of buffer chunks. > + */ > + if (!IS_ALIGNED(cons->preferred_alignment, cons->required_alignment)) > + return -EINVAL; > + > + return 0; > +} > + > +/** > + * sg_alloc_table_from_buf - create an SG table from a buffer > + * > + * @sgt: SG table > + * @buf: buffer you want to create this SG table from > + * @len: length of buf > + * @constraints: optional constraints to take into account when creating > + * the SG table. Can be NULL if no specific constraints are > + * required. > + * @gfp_mask: type of allocation to use when creating the table > + * > + * This function creates an SG table from a buffer, its length and some > + * SG constraints. > + * > + * Note: This function supports vmallocated buffers. > + */ > +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t len, > + const struct sg_constraints *constraints, > + gfp_t gfp_mask) > +{ > + struct sg_constraints cons = { }; > + size_t remaining, chunk_len; > + const void *sg_buf; > + int i, ret; > + > + if (constraints) > + cons = *constraints; > + > + ret = sg_check_constraints(&cons, buf, len); > + if (ret) > + return ret; > + > + sg_buf = buf; > + remaining = len; > + i = 0; > + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) > + i++; > + > + ret = sg_alloc_table(sgt, i, gfp_mask); > + if (ret) > + return ret; > + > + sg_buf = buf; > + remaining = len; > + i = 0; > + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) { > + if (is_vmalloc_addr(sg_buf)) { > + struct page *vm_page; > + > + vm_page = vmalloc_to_page(sg_buf); > + if (!vm_page) { > + ret = -ENOMEM; > + goto err_free_table; > + } > + > + sg_set_page(&sgt->sgl[i], vm_page, chunk_len, > + offset_in_page(sg_buf)); > + } else { > + sg_set_buf(&sgt->sgl[i], sg_buf, chunk_len); > + } > + > + i++; > + } > + > + return 0; > + > +err_free_table: > + sg_free_table(sgt); > + > + return ret; > +} > +EXPORT_SYMBOL(sg_alloc_table_from_buf); > + > void __sg_page_iter_start(struct sg_page_iter *piter, > struct scatterlist *sglist, unsigned int nents, > unsigned long pgoffset)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 556ec1e..4a75362 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -41,6 +41,27 @@ struct sg_table { unsigned int orig_nents; /* original size of list */ }; +/** + * struct sg_constraints - SG constraints structure + * + * @max_chunk_len: maximum chunk buffer length. Each SG entry has to be smaller + * than this value. Zero means no constraint. + * @required_alignment: minimum alignment. Is used for both size and pointer + * alignment. If this constraint is not met, the function + * should return -EINVAL. + * @preferred_alignment: preferred alignment. Mainly used to optimize + * throughput when the DMA engine performs better when + * doing aligned accesses. + * + * This structure is here to help sg_alloc_table_from_buf() create the optimal + * SG list based on DMA engine constraints. + */ +struct sg_constraints { + size_t max_chunk_len; + size_t required_alignment; + size_t preferred_alignment; +}; + /* * Notes on SG table design. * @@ -265,6 +286,9 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, struct page **pages, unsigned int n_pages, unsigned long offset, unsigned long size, gfp_t gfp_mask); +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t len, + const struct sg_constraints *constraints, + gfp_t gfp_mask); size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf, size_t buflen, off_t skip, bool to_buffer); diff --git a/lib/scatterlist.c b/lib/scatterlist.c index bafa993..706b583 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -433,6 +433,148 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, } EXPORT_SYMBOL(sg_alloc_table_from_pages); +static size_t sg_buf_chunk_len(const void *buf, size_t len, + const struct sg_constraints *cons) +{ + size_t chunk_len = len; + + if (cons->max_chunk_len) + chunk_len = min_t(size_t, chunk_len, cons->max_chunk_len); + + if (is_vmalloc_addr(buf)) + chunk_len = min_t(size_t, chunk_len, + PAGE_SIZE - offset_in_page(buf)); + + if (!IS_ALIGNED((unsigned long)buf, cons->preferred_alignment)) { + const void *aligned_buf = PTR_ALIGN(buf, + cons->preferred_alignment); + size_t unaligned_len = (unsigned long)(aligned_buf - buf); + + chunk_len = min_t(size_t, chunk_len, unaligned_len); + } else if (chunk_len > cons->preferred_alignment) { + chunk_len &= ~(cons->preferred_alignment - 1); + } + + return chunk_len; +} + +#define sg_for_each_chunk_in_buf(buf, len, chunk_len, constraints) \ + for (chunk_len = sg_buf_chunk_len(buf, len, constraints); \ + len; \ + len -= chunk_len, buf += chunk_len, \ + chunk_len = sg_buf_chunk_len(buf, len, constraints)) + +static int sg_check_constraints(struct sg_constraints *cons, + const void *buf, size_t len) +{ + if (!cons->required_alignment) + cons->required_alignment = 1; + + if (!cons->preferred_alignment) + cons->preferred_alignment = cons->required_alignment; + + /* Test if buf and len are properly aligned. */ + if (!IS_ALIGNED((unsigned long)buf, cons->required_alignment) || + !IS_ALIGNED(len, cons->required_alignment)) + return -EINVAL; + + /* + * if the buffer has been vmallocated and required_alignment is + * more than PAGE_SIZE we cannot guarantee it. + */ + if (is_vmalloc_addr(buf) && cons->required_alignment > PAGE_SIZE) + return -EINVAL; + + /* + * max_chunk_len has to be aligned to required_alignment to + * guarantee that all buffer chunks are aligned correctly. + */ + if (!IS_ALIGNED(cons->max_chunk_len, cons->required_alignment)) + return -EINVAL; + + /* + * preferred_alignment has to be aligned to required_alignment + * to avoid misalignment of buffer chunks. + */ + if (!IS_ALIGNED(cons->preferred_alignment, cons->required_alignment)) + return -EINVAL; + + return 0; +} + +/** + * sg_alloc_table_from_buf - create an SG table from a buffer + * + * @sgt: SG table + * @buf: buffer you want to create this SG table from + * @len: length of buf + * @constraints: optional constraints to take into account when creating + * the SG table. Can be NULL if no specific constraints are + * required. + * @gfp_mask: type of allocation to use when creating the table + * + * This function creates an SG table from a buffer, its length and some + * SG constraints. + * + * Note: This function supports vmallocated buffers. + */ +int sg_alloc_table_from_buf(struct sg_table *sgt, const void *buf, size_t len, + const struct sg_constraints *constraints, + gfp_t gfp_mask) +{ + struct sg_constraints cons = { }; + size_t remaining, chunk_len; + const void *sg_buf; + int i, ret; + + if (constraints) + cons = *constraints; + + ret = sg_check_constraints(&cons, buf, len); + if (ret) + return ret; + + sg_buf = buf; + remaining = len; + i = 0; + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) + i++; + + ret = sg_alloc_table(sgt, i, gfp_mask); + if (ret) + return ret; + + sg_buf = buf; + remaining = len; + i = 0; + sg_for_each_chunk_in_buf(sg_buf, remaining, chunk_len, &cons) { + if (is_vmalloc_addr(sg_buf)) { + struct page *vm_page; + + vm_page = vmalloc_to_page(sg_buf); + if (!vm_page) { + ret = -ENOMEM; + goto err_free_table; + } + + sg_set_page(&sgt->sgl[i], vm_page, chunk_len, + offset_in_page(sg_buf)); + } else { + sg_set_buf(&sgt->sgl[i], sg_buf, chunk_len); + } + + i++; + } + + return 0; + +err_free_table: + sg_free_table(sgt); + + return ret; +} +EXPORT_SYMBOL(sg_alloc_table_from_buf); + void __sg_page_iter_start(struct sg_page_iter *piter, struct scatterlist *sglist, unsigned int nents, unsigned long pgoffset)
sg_alloc_table_from_buf() provides an easy solution to create an sg_table from a virtual address pointer. This function takes care of dealing with vmallocated buffers, buffer alignment, or DMA engine limitations (maximum DMA transfer size). Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> --- include/linux/scatterlist.h | 24 ++++++++ lib/scatterlist.c | 142 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 166 insertions(+)