diff options
| author | Nicolas Saenz Julienne <nsaenzjulienne@suse.de> | 2019-11-21 10:26:44 +0100 |
|---|---|---|
| committer | Christoph Hellwig <hch@lst.de> | 2019-11-21 18:14:35 +0100 |
| commit | a7ba70f1787f977f970cd116076c6fce4b9e01cc (patch) | |
| tree | 474b2c0bc2201b3d2adde4c7887d4f76d50ac753 /include/linux/device.h | |
| parent | d7293f79caea45c50c0ab4294847e7af96501ced (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 <nsaenzjulienne@suse.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'include/linux/device.h')
| -rw-r--r-- | include/linux/device.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/include/linux/device.h b/include/linux/device.h index 297239a08bb7..e396de656f20 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -1186,8 +1186,8 @@ struct dev_links_info { * @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all * hardware supports 64-bit addresses for consistent allocations * such descriptors. - * @bus_dma_mask: Mask of an upstream bridge or bus which imposes a smaller DMA - * limit than the device itself supports. + * @bus_dma_limit: Limit of an upstream bridge or bus which imposes a smaller + * DMA limit than the device itself supports. * @dma_pfn_offset: offset of DMA memory range relatively of RAM * @dma_parms: A low level driver may set these to teach IOMMU code about * segment limitations. @@ -1270,7 +1270,7 @@ struct device { not all hardware supports 64 bit addresses for consistent allocations such descriptors. */ - u64 bus_dma_mask; /* upstream dma_mask constraint */ + u64 bus_dma_limit; /* upstream dma constraint */ unsigned long dma_pfn_offset; struct device_dma_parameters *dma_parms; |