Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756756AbcCaM37 (ORCPT ); Thu, 31 Mar 2016 08:29:59 -0400 Received: from down.free-electrons.com ([37.187.137.238]:41971 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753669AbcCaM3u (ORCPT ); Thu, 31 Mar 2016 08:29:50 -0400 From: Boris Brezillon To: David Woodhouse , Brian Norris , linux-mtd@lists.infradead.org, Andrew Morton , Dave Gordon Cc: Mark Brown , linux-spi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Vinod Koul , Dan Williams , dmaengine@vger.kernel.org, Mauro Carvalho Chehab , Hans Verkuil , Laurent Pinchart , linux-media@vger.kernel.org, Boris Brezillon , Richard Weinberger , Herbert Xu , "David S. Miller" , linux-crypto@vger.kernel.org, Vignesh R , linux-mm@kvack.org, Joerg Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/4] scatterlist: add sg_alloc_table_from_buf() helper Date: Thu, 31 Mar 2016 14:29:42 +0200 Message-Id: <1459427384-21374-3-git-send-email-boris.brezillon@free-electrons.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1459427384-21374-1-git-send-email-boris.brezillon@free-electrons.com> References: <1459427384-21374-1-git-send-email-boris.brezillon@free-electrons.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7372 Lines: 249 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 --- include/linux/scatterlist.h | 24 ++++++ lib/scatterlist.c | 183 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 207 insertions(+) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 556ec1e..18d1091 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_segment_size: maximum segment 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_segment_size; + 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..9c9746e 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -433,6 +433,189 @@ 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_segment_size) + chunk_len = min_t(size_t, chunk_len, cons->max_segment_size); + + 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) +{ + /* + * We only accept buffers coming from the lowmem, vmalloc and + * highmem regions. + */ + if (!virt_addr_valid(buf) && !is_vmalloc_addr(buf) && + !is_highmem_addr(buf)) + return -EINVAL; + + 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 or kmapped and required_alignment + * is more than PAGE_SIZE we cannot guarantee it. + */ + if (!virt_addr_valid(buf) && cons->required_alignment > PAGE_SIZE) + return -EINVAL; + + /* + * max_segment_size has to be aligned to required_alignment to + * guarantee that all buffer chunks are aligned correctly. + */ + if (!IS_ALIGNED(cons->max_segment_size, 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 buffers coming from the lowmem, vmalloc or + * highmem region. + */ +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 (virt_addr_valid(buf)) { + /* + * Buffer is in lowmem, we can safely call + * sg_set_buf(). + */ + sg_set_buf(&sgt->sgl[i], sg_buf, chunk_len); + } else { + struct page *vm_page; + + /* + * Buffer has been obtained with vmalloc() or kmap(). + * In this case we have to extract the page information + * and use sg_set_page(). + */ + if (is_vmalloc_addr(sg_buf)) + vm_page = vmalloc_to_page(sg_buf); + else + vm_page = kmap_to_page((void *)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)); + } + + 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) -- 2.5.0