| Message ID | 20200925141218.13550-2-m.szyprowski@samsung.com |
|---|---|
| State | New |
| Headers | show |
| Series | IOMMU-DMA - support old allocation algorithm used on ARM | expand |
> #define DMA_ATTR_PRIVILEGED (1UL << 9) > +/* > + * DMA_ATTR_LOW_ADDRESS: used to indicate that the buffer should be allocated > + * at the lowest possible DMA address, usually just at the beginning of the > + * DMA/IOVA address space ('first-fit' allocation algorithm). > + */ > +#define DMA_ATTR_LOW_ADDRESS (1UL << 10) I think we need better comments explaining that this is best effort and only applies to DMA API implementations that actually have an allocatable IOVA space.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index bb138ac6f5e6..c8c568ba375b 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -66,6 +66,12 @@ * at least read-only at lesser-privileged levels). */ #define DMA_ATTR_PRIVILEGED (1UL << 9) +/* + * DMA_ATTR_LOW_ADDRESS: used to indicate that the buffer should be allocated + * at the lowest possible DMA address, usually just at the beginning of the + * DMA/IOVA address space ('first-fit' allocation algorithm). + */ +#define DMA_ATTR_LOW_ADDRESS (1UL << 10) /* * A dma_addr_t can hold any valid DMA or bus address for the platform.
Some devices require to allocate a special buffer (usually for the firmware) just at the beginning of the address space to ensure that all further allocations can be expressed as a positive offset from that special buffer. When IOMMU is used for managing the DMA address space, such requirement can be easily fulfilled, simply by enforcing the 'first-fit' IOVA allocation algorithm. This patch adds a DMA attribute for such case. Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> --- include/linux/dma-mapping.h | 6 ++++++ 1 file changed, 6 insertions(+)