path: root/arch/nds32
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authorNicolas Saenz Julienne <>2019-11-21 10:26:44 +0100
committerChristoph Hellwig <>2019-11-21 18:14:35 +0100
commita7ba70f1787f977f970cd116076c6fce4b9e01cc (patch)
tree474b2c0bc2201b3d2adde4c7887d4f76d50ac753 /arch/nds32
parentd7293f79caea45c50c0ab4294847e7af96501ced (diff)
dma-mapping: treat dev->bus_dma_mask as a DMA limit
Using a mask to represent bus DMA constraints has a set of limitations. The biggest one being it can only hold a power of two (minus one). The DMA mapping code is already aware of this and treats dev->bus_dma_mask as a limit. This quirk is already used by some architectures although still rare. With the introduction of the Raspberry Pi 4 we've found a new contender for the use of bus DMA limits, as its PCIe bus can only address the lower 3GB of memory (of a total of 4GB). This is impossible to represent with a mask. To make things worse the device-tree code rounds non power of two bus DMA limits to the next power of two, which is unacceptable in this case. In the light of this, rename dev->bus_dma_mask to dev->bus_dma_limit all over the tree and treat it as such. Note that dev->bus_dma_limit should contain the higher accessible DMA address. Signed-off-by: Nicolas Saenz Julienne <> Reviewed-by: Robin Murphy <> Signed-off-by: Christoph Hellwig <>
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