From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH 01/23] dma-mapping: provide a generic DMA_MAPPING_ERROR Date: Tue, 4 Dec 2018 16:41:34 +0000 Message-ID: <653ca801-63a1-3c19-ee09-ade19fa2bbb8@arm.com> References: <20181130132231.16512-1-hch@lst.de> <20181130132231.16512-2-hch@lst.de> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181130132231.16512-2-hch@lst.de> Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Christoph Hellwig , iommu@lists.linux-foundation.org Cc: linux-arch@vger.kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, Linus Torvalds , x86@kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, David Woodhouse , linux-arm-kernel@lists.infradead.org On 30/11/2018 13:22, Christoph Hellwig wrote: > Error handling of the dma_map_single and dma_map_page APIs is a little > problematic at the moment, in that we use different encodings in the > returned dma_addr_t to indicate an error. That means we require an > additional indirect call to figure out if a dma mapping call returned > an error, and a lot of boilerplate code to implement these semantics. > > Instead return the maximum addressable value as the error. As long > as we don't allow mapping single-byte ranges with single-byte alignment > this value can never be a valid return. Additionaly if drivers do > not check the return value from the dma_map* routines this values means > they will generally not be pointed to actual memory. > > Once the default value is added here we can start removing the > various mapping_error methods and just rely on this generic check. > > Signed-off-by: Christoph Hellwig > --- > include/linux/dma-mapping.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 0f81c713f6e9..46bd612d929e 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -133,6 +133,8 @@ struct dma_map_ops { > u64 (*get_required_mask)(struct device *dev); > }; > > +#define DMA_MAPPING_ERROR (~(dma_addr_t)0) > + > extern const struct dma_map_ops dma_direct_ops; > extern const struct dma_map_ops dma_virt_ops; > > @@ -576,6 +578,10 @@ static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr) > const struct dma_map_ops *ops = get_dma_ops(dev); > > debug_dma_mapping_error(dev, dma_addr); > + > + if (dma_addr == DMA_MAPPING_ERROR) > + return 1; > + > if (ops->mapping_error) > return ops->mapping_error(dev, dma_addr); > return 0; I'd have been inclined to put the default check here, i.e. - return 0 + return dma_addr == DMA_MAPPING_ERROR such that the callback retains full precedence and we don't have to deal with the non-trivial removals immediately if it comes to it. Not that it makes a vast difference though, so either way, Reviewed-by: Robin Murphy