| Message ID | 1459352394-22810-5-git-send-email-boris.brezillon@free-electrons.com |
|---|---|
| State | Deferred |
| Headers | show |
On Wed, Mar 30, 2016 at 05:39:51PM +0200, 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). This seems nice. Should we also have a further helper on top of this which will get constraints from a dmaengine, it seems like it'd be a common need?
On Wed, 30 Mar 2016 09:51:43 -0700 Mark Brown <broonie@kernel.org> wrote: > On Wed, Mar 30, 2016 at 05:39:51PM +0200, 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). > > This seems nice. Should we also have a further helper on top of this > which will get constraints from a dmaengine, it seems like it'd be a > common need? Yep, we could create a wrapper extracting dma_slave caps info, converting it to sg_constraints and calling sg_alloc_table_from_buf(). But let's try to get this function accepted first, and I'll send another patch providing this wrapper. BTW, do you see other things that should be added in sg_constraints?
On Wed, Mar 30, 2016 at 08:18:31PM +0200, Boris Brezillon wrote:
> BTW, do you see other things that should be added in sg_constraints?
It looked to do everything SPI does which is everything I know about.
Hi, On 03/30/2016 09:09 PM, Boris BREZILLON wrote: [...] > +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); > + } > + If the buf address is in PKMAP_BASE - PAGE_OFFSET-1 region (I have observed that JFFS2 FS provides buffers in above region to MTD layer), if CONFIG_DEBUG_SG is set then sg_set_buf() will throw a BUG_ON() as virt_addr_is_valid() will return false. Is there a sane way to handle buffers of PKMAP_BASE region with sg_* APIs? Or, is the function sg_alloc_table_from_buf() not to be used with such buffers?
Hi Vignesh, On Thu, 31 Mar 2016 10:26:59 +0530 Vignesh R <vigneshr@ti.com> wrote: > Hi, > > On 03/30/2016 09:09 PM, Boris BREZILLON wrote: > > [...] > > > +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); > > + } > > + > > If the buf address is in PKMAP_BASE - PAGE_OFFSET-1 region (I have > observed that JFFS2 FS provides buffers in above region to MTD layer), > if CONFIG_DEBUG_SG is set then sg_set_buf() will throw a BUG_ON() as > virt_addr_is_valid() will return false. Is there a sane way to handle > buffers of PKMAP_BASE region with sg_* APIs? > Or, is the function sg_alloc_table_from_buf() not to be used with such > buffers? It should be usable with kmapped buffers too: I'll provide a new version to support that. That makes me realize I'm not checking the virtual address consistency in sg_check_constraints(). Thanks, Boris
On 30/03/16 19:18, Boris Brezillon wrote: > On Wed, 30 Mar 2016 09:51:43 -0700 > Mark Brown <broonie@kernel.org> wrote: > >> On Wed, Mar 30, 2016 at 05:39:51PM +0200, 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). >> >> This seems nice. Should we also have a further helper on top of this >> which will get constraints from a dmaengine, it seems like it'd be a >> common need? > > Yep, we could create a wrapper extracting dma_slave caps info, > converting it to sg_constraints and calling sg_alloc_table_from_buf(). > But let's try to get this function accepted first, and I'll send another > patch providing this wrapper. > > BTW, do you see other things that should be added in sg_constraints? > You could compare with the things Solaris uses to describe the restrictions on a DMA binding ... http://docs.oracle.com/cd/E23824_01/html/821-1478/ddi-dma-attr-9s.html#REFMAN9Sddi-dma-attr-9s .Dave.
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 004fc70..94776ff 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -433,6 +433,167 @@ 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)) { + unsigned long offset_in_page = offset_in_page(buf); + size_t contig_len = PAGE_SIZE - offset_in_page; + unsigned long phys = vmalloc_to_pfn(buf) - offset_in_page; + const void *contig_ptr = buf + contig_len; + + /* + * Vmalloced buffer might be composed of several physically + * contiguous pages. Avoid extra scattergather entries in + * this case. + */ + while (contig_len < chunk_len) { + if (phys + PAGE_SIZE != vmalloc_to_pfn(contig_ptr)) + break; + + contig_len += PAGE_SIZE; + contig_ptr += PAGE_SIZE; + phys += PAGE_SIZE; + } + + chunk_len = min_t(size_t, chunk_len, contig_len); + } + + 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 and physically contiguous 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 | 161 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 185 insertions(+)