From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753656AbbAUS5N (ORCPT ); Wed, 21 Jan 2015 13:57:13 -0500 Received: from service87.mimecast.com ([91.220.42.44]:54125 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750917AbbAUS5G convert rfc822-to-8bit (ORCPT ); Wed, 21 Jan 2015 13:57:06 -0500 Message-ID: <54BFF679.6010705@arm.com> Date: Wed, 21 Jan 2015 18:56:57 +0000 From: Robin Murphy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 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: "t.stanislaws@samsung.com" , "linaro-kernel@lists.linaro.org" , "robdclark@gmail.com" , "daniel@ffwll.ch" , "m.szyprowski@samsung.com" Subject: Re: [RFCv2 1/2] device: add dma_params->max_segment_count References: <1421813807-9178-1-git-send-email-sumit.semwal@linaro.org> <1421813807-9178-2-git-send-email-sumit.semwal@linaro.org> In-Reply-To: <1421813807-9178-2-git-send-email-sumit.semwal@linaro.org> X-OriginalArrivalTime: 21 Jan 2015 18:57:01.0617 (UTC) FILETIME=[0A3D2210:01D035AC] X-MC-Unique: 115012118570400201 Content-Type: text/plain; charset=WINDOWS-1252; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > + > +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 ? >