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[216.228.112.21]) by smtp.gmail.com with ESMTPSA id v75sm1510501pjb.35.2020.05.19.01.04.10 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Tue, 19 May 2020 01:04:10 -0700 (PDT) Date: Tue, 19 May 2020 01:04:08 -0700 From: Nicolin Chen To: robin.murphy@arm.com, m.szyprowski@samsung.com, hch@lst.de Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org Subject: Re: [RFC/RFT][PATCH v2] dma-mapping: set default segment_boundary_mask to ULONG_MAX Message-ID: <20200519080408.GA15325@Asurada-Nvidia> References: <20200406210643.20665-1-nicoleotsuka@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200406210643.20665-1-nicoleotsuka@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Robin/Christoph, This v2 was sent a while ago. I know that we had a concern, yet will we have a closure whether merging it or not? Thanks! Nic On Mon, Apr 06, 2020 at 02:06:43PM -0700, Nicolin Chen wrote: > The default segment_boundary_mask was set to DMA_BIT_MAKS(32) > a decade ago by referencing SCSI/block subsystem, as a 32-bit > mask was good enough for most of the devices. > > Now more and more drivers set dma_masks above DMA_BIT_MAKS(32) > while only a handful of them call dma_set_seg_boundary(). This > means that most drivers have a 4GB segmention boundary because > DMA API returns a 32-bit default value, though they might not > really have such a limit. > > The default segment_boundary_mask should mean "no limit" since > the device doesn't explicitly set the mask. But a 32-bit mask > certainly limits those devices capable of 32+ bits addressing. > > So this patch sets default segment_boundary_mask to ULONG_MAX. > > Signed-off-by: Nicolin Chen > --- > Changelog: > v1->v2 > * Followed Robin's comments to revise the commit message by > dropping one paragraph of not-entirely-true justification > (no git-diff level change, so please ack if you tested v1) > > include/linux/dma-mapping.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 330ad58fbf4d..ff8cefe85f30 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -736,7 +736,7 @@ static inline unsigned long dma_get_seg_boundary(struct device *dev) > { > if (dev->dma_parms && dev->dma_parms->segment_boundary_mask) > return dev->dma_parms->segment_boundary_mask; > - return DMA_BIT_MASK(32); > + return ULONG_MAX; > } > > static inline int dma_set_seg_boundary(struct device *dev, unsigned long mask) > -- > 2.17.1 >