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dma-mapping: treat dev->bus_dma_mask as a DMA limit

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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>
This commit is contained in:
Nicolas Saenz Julienne
2019-11-21 10:26:44 +01:00
committed by Christoph Hellwig
parent d7293f79ca
commit a7ba70f178
13 changed files with 46 additions and 53 deletions
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6
include/linux/device.h
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@@ -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;

2
include/linux/dma-direct.h
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@@ -63,7 +63,7 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
min(addr, end) < phys_to_dma(dev, PFN_PHYS(min_low_pfn)))
return false;
return end <= min_not_zero(*dev->dma_mask, dev->bus_dma_mask);
return end <= min_not_zero(*dev->dma_mask, dev->bus_dma_limit);
}
u64 dma_direct_get_required_mask(struct device *dev);

2
include/linux/dma-mapping.h
View File

@@ -697,7 +697,7 @@ static inline int dma_coerce_mask_and_coherent(struct device *dev, u64 mask)
*/
static inline bool dma_addressing_limited(struct device *dev)
{
return min_not_zero(dma_get_mask(dev), dev->bus_dma_mask) <
return min_not_zero(dma_get_mask(dev), dev->bus_dma_limit) <
dma_get_required_mask(dev);
}