On few architectures, there are few restrictions on DMAble area of system RAM. That also means that devices needs to know about this restrictions so that the dma_masks can be updated accordingly and dma address translation helpers can add/subtract the dma offset.
In most of cases DMA addresses can be performed using offset value of Bus address space relatively to physical address space as following: PFN->DMA: __pfn_to_phys(pfn + [-]dma_pfn_offset) DMA->PFN: __phys_to_pfn(dma_addr) + [-]dma_pfn_offset So we introduce per device dma_pfn_offset which can be popullated by architecture init code while creating the devices. Cc: Greg Kroah-Hartman <[email protected]> Cc: Russell King <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Olof Johansson <[email protected]> Cc: Grant Likely <[email protected]> Cc: Rob Herring <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Linus Walleij <[email protected]> Signed-off-by: Grygorii Strashko <[email protected]> Signed-off-by: Santosh Shilimkar <[email protected]> --- include/linux/device.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/device.h b/include/linux/device.h index 233bbbe..85a52d6 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -691,6 +691,7 @@ struct acpi_dev_node { * @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all * hardware supports 64-bit addresses for consistent allocations * such descriptors. + * @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. * @dma_pools: Dma pools (if dma'ble device). @@ -756,6 +757,7 @@ struct device { not all hardware supports 64 bit addresses for consistent allocations such descriptors. */ + unsigned long dma_pfn_offset; struct device_dma_parameters *dma_parms; -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
