From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f45.google.com (mail-oi0-f45.google.com [209.85.218.45]) by kanga.kvack.org (Postfix) with ESMTP id 2B07D6B0032 for ; Wed, 21 Jan 2015 22:46:23 -0500 (EST) Received: by mail-oi0-f45.google.com with SMTP id g201so7324920oib.4 for ; Wed, 21 Jan 2015 19:46:22 -0800 (PST) Received: from mail-ob0-f177.google.com (mail-ob0-f177.google.com. [209.85.214.177]) by mx.google.com with ESMTPS id h10si10320134obx.98.2015.01.21.19.46.22 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 21 Jan 2015 19:46:22 -0800 (PST) Received: by mail-ob0-f177.google.com with SMTP id uy5so42631811obc.8 for ; Wed, 21 Jan 2015 19:46:22 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <54BFF679.6010705@arm.com> References: <1421813807-9178-1-git-send-email-sumit.semwal@linaro.org> <1421813807-9178-2-git-send-email-sumit.semwal@linaro.org> <54BFF679.6010705@arm.com> From: Sumit Semwal Date: Thu, 22 Jan 2015 09:16:01 +0530 Message-ID: Subject: Re: [RFCv2 1/2] device: add dma_params->max_segment_count Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Robin Murphy Cc: "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" , "t.stanislaws@samsung.com" , "linaro-kernel@lists.linaro.org" , "robdclark@gmail.com" , "daniel@ffwll.ch" , "m.szyprowski@samsung.com" Hi Robin! On 22 January 2015 at 00:26, Robin Murphy wrote: > Hi Sumit, > > > On 21/01/15 04:16, 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 on the first version] >> Signed-off-by: Sumit Semwal >> --- >> 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 fb50673..a32f9b6 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 c3007cb..38e2835 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) >> +{ >> + return dev->dma_parms ? >> + dev->dma_parms->max_segment_count : >> + DMA_SEGMENTS_MAX_SEG_COUNT; >> +} > > > I know this copies the style of the existing code, but unfortunately it also > copies the subtle brokenness. Plenty of drivers seem to set up a dma_parms > struct just for max_segment_size, thus chances are you'll come across a > max_segment_count of 0 sooner or later. How badly is that going to break > things? I posted a fix recently[1] having hit this problem with > segment_boundary_mask in IOMMU code. > Thanks very much for reviewing this code; and apologies for missing your patch that you mentioned here; sure, I will update my patch accordingly as well. >> + >> +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; >> + } else > > > This "else" is just as unnecessary as the other two I've taken out ;) > > > Robin. > > [1]:http://article.gmane.org/gmane.linux.kernel.iommu/8175/ > > >> + return -EIO; >> +} >> + >> static inline unsigned long dma_get_seg_boundary(struct device *dev) >> { >> return dev->dma_parms ? >> > > BR, Sumit. -- 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