From mboxrd@z Thu Jan 1 00:00:00 1970 From: nikita.yoush@cogentembedded.com (Nikita Yushchenko) Date: Wed, 4 Jan 2017 09:24:09 +0300 Subject: [PATCH 1/2] arm64: dma_mapping: allow PCI host driver to limit DMA mask In-Reply-To: <5224989.KFLmAz9Gqk@wuerfel> References: <1483044304-2085-1-git-send-email-nikita.yoush@cogentembedded.com> <20170103184444.GP6986@arm.com> <5224989.KFLmAz9Gqk@wuerfel> Message-ID: <4bbc3494-bf95-9765-ccaf-cc3b3e1cd297@cogentembedded.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > commit 9a57d58d116800a535510053136c6dd7a9c26e25 > Author: Arnd Bergmann > Date: Tue Nov 17 14:06:55 2015 +0100 > > [EXPERIMENTAL] ARM64: check implement dma_set_mask > > Needs work for coherent mask > > Signed-off-by: Arnd Bergmann Unfortunately this is far incomplete > @@ -957,6 +983,18 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size, > if (!dev->archdata.dma_ops) > dev->archdata.dma_ops = &swiotlb_dma_ops; > > + /* > + * we don't yet support buses that have a non-zero mapping. > + * Let's hope we won't need it > + */ > + WARN_ON(dma_base != 0); > + > + /* > + * Whatever the parent bus can set. A device must not set > + * a DMA mask larger than this. > + */ > + dev->archdata.parent_dma_mask = size; > + ... because size/mask passed here for PCI devices are meaningless. For OF platforms, this is called via of_dma_configure(), that checks dma-ranges of node that is *parent* for host bridge. Host bridge currently does not control this at all. In current device trees no dma-ranges is defined for nodes that are parents to pci host bridges. This will make of_dma_configure() to fall back to 32-bit size for all devices on all current platforms. Thus applying this patch will immediately break 64-bit dma masks on all hardware that supports it. Also related: dma-ranges property used by several pci host bridges is *not* compatible with "legacy" dma-ranges parsed by of_get_dma_range() - former uses additional flags word at beginning.