From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH 31/33] dma-direct: reject too small dma masks Date: Wed, 10 Jan 2018 11:49:34 +0000 Message-ID: <0bcca030-a8da-c34a-a905-707986689f33@arm.com> References: <20180110080027.13879-1-hch@lst.de> <20180110080027.13879-32-hch@lst.de> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180110080027.13879-32-hch@lst.de> Content-Language: en-GB Sender: linux-m68k-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-mips@linux-mips.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Guan Xuetao , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, linux-hexagon@vger.kernel.org, x86@kernel.org, Konrad Rzeszutek Wilk , linux-snps-arc@lists.infradead.org, linux-m68k@lists.linux-m68k.org, patches@groups.riscv.org, linux-metag@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Michal Simek , linux-parisc@vger.kernel.org, linux-cris-kernel@axis.com, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linuxppc-dev@lists.ozlabs.org On 10/01/18 08:00, Christoph Hellwig wrote: > Signed-off-by: Christoph Hellwig > --- > include/linux/dma-direct.h | 1 + > lib/dma-direct.c | 19 +++++++++++++++++++ > 2 files changed, 20 insertions(+) > > diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h > index 4788bf0bf683..bcdb1a3e4b1f 100644 > --- a/include/linux/dma-direct.h > +++ b/include/linux/dma-direct.h > @@ -42,5 +42,6 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle, > gfp_t gfp, unsigned long attrs); > void dma_direct_free(struct device *dev, size_t size, void *cpu_addr, > dma_addr_t dma_addr, unsigned long attrs); > +int dma_direct_supported(struct device *dev, u64 mask); > > #endif /* _LINUX_DMA_DIRECT_H */ > diff --git a/lib/dma-direct.c b/lib/dma-direct.c > index 784a68dfdbe3..40b1f92f2214 100644 > --- a/lib/dma-direct.c > +++ b/lib/dma-direct.c > @@ -122,6 +122,24 @@ static int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, > return nents; > } > > +int dma_direct_supported(struct device *dev, u64 mask) > +{ > +#ifdef CONFIG_ZONE_DMA > + if (mask < DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) > + return 0; > +#else > + /* > + * Because 32-bit DMA masks are so common we expect every architecture > + * to be able to satisfy them - either by not supporting more physical > + * memory, or by providing a ZONE_DMA32. If neither is the case, the > + * architecture needs to use an IOMMU instead of the direct mapping. > + */ > + if (mask < DMA_BIT_MASK(32)) > + return 0; Do you think it's worth the effort to be a little more accommodating here? i.e.: return dma_max_pfn(dev) >= max_pfn; We seem to have a fair few 28-31 bit masks for older hardware which probably associates with host systems packing equivalently small amounts of RAM. Otherwise though, Reviewed-by: Robin Murphy Robin. > +#endif > + return 1; > +} > + > static int dma_direct_mapping_error(struct device *dev, dma_addr_t dma_addr) > { > return dma_addr == DIRECT_MAPPING_ERROR; > @@ -132,6 +150,7 @@ const struct dma_map_ops dma_direct_ops = { > .free = dma_direct_free, > .map_page = dma_direct_map_page, > .map_sg = dma_direct_map_sg, > + .dma_supported = dma_direct_supported, > .mapping_error = dma_direct_mapping_error, > }; > EXPORT_SYMBOL(dma_direct_ops); >