From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id C66056B002C for ; Fri, 2 Mar 2012 06:08:07 -0500 (EST) Received: from euspt1 (mailout2.w1.samsung.com [210.118.77.12]) by mailout2.w1.samsung.com (iPlanet Messaging Server 5.2 Patch 2 (built Jul 14 2004)) with ESMTP id <0M0900FLC89HQ8@mailout2.w1.samsung.com> for linux-mm@kvack.org; Fri, 02 Mar 2012 11:08:05 +0000 (GMT) Received: from linux.samsung.com ([106.116.38.10]) by spt1.w1.samsung.com (iPlanet Messaging Server 5.2 Patch 2 (built Jul 14 2004)) with ESMTPA id <0M09003OZ89HOK@spt1.w1.samsung.com> for linux-mm@kvack.org; Fri, 02 Mar 2012 11:08:05 +0000 (GMT) Date: Fri, 02 Mar 2012 12:07:59 +0100 From: Marek Szyprowski Subject: RE: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper In-reply-to: Message-id: <015101ccf864$bacb1070$30613150$%szyprowski@samsung.com> MIME-version: 1.0 Content-type: text/plain; charset=iso-8859-2 Content-language: pl Content-transfer-encoding: quoted-printable References: <1330527862-16234-1-git-send-email-m.szyprowski@samsung.com> <1330527862-16234-10-git-send-email-m.szyprowski@samsung.com> Sender: owner-linux-mm@kvack.org List-ID: To: 'KyongHo Cho' Cc: linux-arm-kernel@lists.infradead.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-samsung-soc@vger.kernel.org, iommu@lists.linux-foundation.org, 'Shariq Hasnain' , 'Arnd Bergmann' , 'Benjamin Herrenschmidt' , 'Krishna Reddy' , 'Kyungmin Park' , Andrzej Pietrasiewicz , 'Russell King - ARM Linux' , 'Chunsang Jeong' Hello, On Friday, March 02, 2012 9:06 AM KyongHo Cho wrote: > On Thu, Mar 1, 2012 at 12:04 AM, Marek Szyprowski > wrote: > > +/** > > + * arm_iommu_map_sg - map a set of SG buffers for streaming mode = DMA > > + * @dev: valid struct device pointer > > + * @sg: list of buffers > > + * @nents: number of buffers to map > > + * @dir: DMA transfer direction > > + * > > + * Map a set of buffers described by scatterlist in streaming mode = for DMA. > > + * The scatter gather list elements are merged together (if = possible) and > > + * tagged with the appropriate dma address and length. They are = obtained via > > + * sg_dma_{address,length}. > > + */ > > +int arm_iommu_map_sg(struct device *dev, struct scatterlist *sg, = int nents, > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0enum dma_data_direction = dir, struct dma_attrs *attrs) > > +{ > > + =A0 =A0 =A0 struct scatterlist *s =3D sg, *dma =3D sg, *start =3D = sg; > > + =A0 =A0 =A0 int i, count =3D 0; > > + =A0 =A0 =A0 unsigned int offset =3D s->offset; > > + =A0 =A0 =A0 unsigned int size =3D s->offset + s->length; > > + =A0 =A0 =A0 unsigned int max =3D dma_get_max_seg_size(dev); > > + > > + =A0 =A0 =A0 for (i =3D 1; i < nents; i++) { > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 s->dma_address =3D ARM_DMA_ERROR; > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 s->dma_length =3D 0; > > + > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 s =3D sg_next(s); > > + > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (s->offset || (size & ~PAGE_MASK) = || size + s->length > max) { > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if = (__map_sg_chunk(dev, start, size, &dma->dma_address, > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 dir) < 0) > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto = bad_mapping; > > + > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 dma->dma_address +=3D = offset; > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 dma->dma_length =3D = size - offset; > > + > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 size =3D offset =3D = s->offset; > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 start =3D s; > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 dma =3D sg_next(dma); > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 count +=3D 1; > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 } > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 size +=3D s->length; > > + =A0 =A0 =A0 } > > + =A0 =A0 =A0 if (__map_sg_chunk(dev, start, size, = &dma->dma_address, dir) < 0) > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto bad_mapping; > > + > > + =A0 =A0 =A0 dma->dma_address +=3D offset; > > + =A0 =A0 =A0 dma->dma_length =3D size - offset; > > + > > + =A0 =A0 =A0 return count+1; > > + > > +bad_mapping: > > + =A0 =A0 =A0 for_each_sg(sg, s, count, i) > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 __iommu_remove_mapping(dev, = sg_dma_address(s), sg_dma_len(s)); > > + =A0 =A0 =A0 return 0; > > +} > > + > This looks that the given sg list specifies the list of physical > memory chunks and > the list of IO virtual memory chunks at the same time after calling > arm_dma_map_sg(). > It can happen that dma_address and dma_length of a sg entry does not > correspond to > physical memory information of the sg entry. Right, that's how it is designed. If fact sg entries describes 2 = independent=20 lists - one for physical memory chunks and one for virtual memory = chunks.=20 It might happen that the whole scattered physical memory can be mapped = into contiguous virtual memory chunk, what result in only one element = describing the io dma addresses. Here is the respective paragraph from=20 Documentation/DMA-API-HOWTO.txt (lines 511-517): 'The implementation is free to merge several consecutive sglist entries into one (e.g. if DMA mapping is done with PAGE_SIZE granularity, any consecutive sglist entries can be merged into one provided the first one ends and the second one starts on a page boundary - in fact this is a = huge advantage for cards which either cannot do scatter-gather or have very limited number of scatter-gather entries) and returns the actual number of sg entries it mapped them to. On failure 0 is returned.' > I think it is beneficial for handling IO virtual memory. >=20 > However, I worry about any other problems caused by a single sg entry = contains > information from 2 different context. What do you mean by the 'context'. DMA mapping assumes that a single = call to=20 dma_map_sg maps a single memory buffer. Best regards --=20 Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org