On Tue, 8 Mar 2016 12:15:12 +0100 Boris Brezillon <boris.brezil...@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.brezil...@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) -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.