From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f173.google.com (mail-pd0-f173.google.com [209.85.192.173]) by kanga.kvack.org (Postfix) with ESMTP id 7C3836B0038 for ; Wed, 28 Jan 2015 09:09:37 -0500 (EST) Received: by mail-pd0-f173.google.com with SMTP id fp1so25903787pdb.4 for ; Wed, 28 Jan 2015 06:09:37 -0800 (PST) Received: from mailout2.w1.samsung.com (mailout2.w1.samsung.com. [210.118.77.12]) by mx.google.com with ESMTPS id kk8si5797335pdb.218.2015.01.28.06.09.35 for (version=TLSv1 cipher=RC4-MD5 bits=128/128); Wed, 28 Jan 2015 06:09:36 -0800 (PST) Received: from eucpsbgm1.samsung.com (unknown [203.254.199.244]) by mailout2.w1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0NIW0033U4UNMP30@mailout2.w1.samsung.com> for linux-mm@kvack.org; Wed, 28 Jan 2015 14:13:35 +0000 (GMT) Message-id: <54C8ED9A.9070201@samsung.com> Date: Wed, 28 Jan 2015 15:09:30 +0100 From: Marek Szyprowski MIME-version: 1.0 Subject: Re: [RFCv3 1/2] device: add dma_params->max_segment_count References: <1422347154-15258-1-git-send-email-sumit.semwal@linaro.org> In-reply-to: <1422347154-15258-1-git-send-email-sumit.semwal@linaro.org> Content-type: text/plain; charset=utf-8; format=flowed Content-transfer-encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Sumit Semwal , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Cc: linaro-kernel@lists.linaro.org, robdclark@gmail.com, daniel@ffwll.ch, stanislawski.tomasz@googlemail.com, robin.murphy@arm.com Hello, On 2015-01-27 09:25, Sumit Semwal wrote: > From: Rob Clark > > For devices which have constraints about maximum number of segments in > an sglist. For example, a device which could only deal with contiguous > buffers would set max_segment_count to 1. > > The initial motivation is for devices sharing buffers via dma-buf, > to allow the buffer exporter to know the constraints of other > devices which have attached to the buffer. The dma_mask and fields > in 'struct device_dma_parameters' tell the exporter everything else > that is needed, except whether the importer has constraints about > maximum number of segments. > > Signed-off-by: Rob Clark > [sumits: Minor updates wrt comments] > Signed-off-by: Sumit Semwal This feature is definitely needed to start thinking of real buffer sharing between devices. Acked-by: Marek Szyprowski > --- > > v3: include Robin Murphy's fix[1] for handling '0' as a value for > max_segment_count > v2: minor updates wrt comments on the first version > > [1]: http://article.gmane.org/gmane.linux.kernel.iommu/8175/ > > include/linux/device.h | 1 + > include/linux/dma-mapping.h | 19 +++++++++++++++++++ > 2 files changed, 20 insertions(+) > > diff --git a/include/linux/device.h b/include/linux/device.h > index fb506738f7b7..a32f9b67315c 100644 > --- a/include/linux/device.h > +++ b/include/linux/device.h > @@ -647,6 +647,7 @@ struct device_dma_parameters { > * sg limitations. > */ > unsigned int max_segment_size; > + unsigned int max_segment_count; /* INT_MAX for unlimited */ > unsigned long segment_boundary_mask; > }; > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index c3007cb4bfa6..d3351a36d5ec 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -154,6 +154,25 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev, > return -EIO; > } > > +#define DMA_SEGMENTS_MAX_SEG_COUNT ((unsigned int) INT_MAX) > + > +static inline unsigned int dma_get_max_seg_count(struct device *dev) > +{ > + if (dev->dma_parms && dev->dma_parms->max_segment_count) > + return dev->dma_parms->max_segment_count; > + return DMA_SEGMENTS_MAX_SEG_COUNT; > +} > + > +static inline int dma_set_max_seg_count(struct device *dev, > + unsigned int count) > +{ > + if (dev->dma_parms) { > + dev->dma_parms->max_segment_count = count; > + return 0; > + } > + return -EIO; > +} > + > static inline unsigned long dma_get_seg_boundary(struct device *dev) > { > return dev->dma_parms ? Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland -- 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/ . Don't email: email@kvack.org