From mboxrd@z Thu Jan 1 00:00:00 1970 From: robin.murphy@arm.com (Robin Murphy) Date: Mon, 20 Jul 2015 18:00:57 +0100 Subject: [PATCH 1/2] arm64: dma-mapping: implement dma_get_sgtable() In-Reply-To: <20150720163645.GM9908@arm.com> References: <65a75c2ea16d0fff8e8ec18a8f42e204c33249ed.1437148528.git.robin.murphy@arm.com> <20150720163645.GM9908@arm.com> Message-ID: <55AD2949.2040401@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Will, On 20/07/15 17:36, Will Deacon wrote: > On Fri, Jul 17, 2015 at 04:58:21PM +0100, Robin Murphy wrote: >> The default dma_common_get_sgtable() implementation relies on the CPU >> address of the buffer being a regular lowmem address. This is not always >> the case on arm64, since allocations from the various DMA pools may have >> remapped vmalloc addresses, rendering the use of virt_to_page() invalid. >> >> Fix this by providing our own implementation based on the fact that we >> can safely derive a physical address from the DMA address in both cases. >> >> CC: Jon Medhurst >> Signed-off-by: Robin Murphy >> --- >> arch/arm64/mm/dma-mapping.c | 14 ++++++++++++++ >> 1 file changed, 14 insertions(+) >> >> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c >> index d16a1ce..4b9b600 100644 >> --- a/arch/arm64/mm/dma-mapping.c >> +++ b/arch/arm64/mm/dma-mapping.c >> @@ -337,10 +337,24 @@ static int __swiotlb_mmap(struct device *dev, >> return __dma_common_mmap(dev, vma, cpu_addr, dma_addr, size); >> } >> >> +int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt, >> + void *cpu_addr, dma_addr_t handle, size_t size, >> + struct dma_attrs *attrs) >> +{ >> + int ret = sg_alloc_table(sgt, 1, GFP_KERNEL); >> + >> + if (!ret) >> + sg_set_page(sgt->sgl, phys_to_page(dma_to_phys(dev, handle)), >> + PAGE_ALIGN(size), 0); >> + >> + return ret; >> +} > > Any reason not to do this in dma_common_get_sgtable? Summarising the discussion over at [1], most architectures seem to depend on dma_common_get_sgtable, but only a handful implement dma_to_phys (plus this approach seems to match the original intent). There doesn't seem to be a nice solution for doing this in common code without a big cross-architecture patch, and it's somewhat questionable how widely this is actually needed. Robin. [1]:http://thread.gmane.org/gmane.linux.kernel/1998795 > > Will >