diff options
Diffstat (limited to 'Documentation/DMA-attributes.txt')
| -rw-r--r-- | Documentation/DMA-attributes.txt | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index 44c6bc496eee..8f8d97f65d73 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -1,5 +1,6 @@ - DMA attributes - ============== +============== +DMA attributes +============== This document describes the semantics of the DMA attributes that are defined in linux/dma-mapping.h. @@ -108,6 +109,7 @@ This is a hint to the DMA-mapping subsystem that it's probably not worth the time to try to allocate memory to in a way that gives better TLB efficiency (AKA it's not worth trying to build the mapping out of larger pages). You might want to specify this if: + - You know that the accesses to this memory won't thrash the TLB. You might know that the accesses are likely to be sequential or that they aren't sequential but it's unlikely you'll ping-pong @@ -121,11 +123,12 @@ pages). You might want to specify this if: the mapping to have a short lifetime then it may be worth it to optimize allocation (avoid coming up with large pages) instead of getting the slight performance win of larger pages. + Setting this hint doesn't guarantee that you won't get huge pages, but it means that we won't try quite as hard to get them. -NOTE: At the moment DMA_ATTR_ALLOC_SINGLE_PAGES is only implemented on ARM, -though ARM64 patches will likely be posted soon. +.. note:: At the moment DMA_ATTR_ALLOC_SINGLE_PAGES is only implemented on ARM, + though ARM64 patches will likely be posted soon. DMA_ATTR_NO_WARN ---------------- @@ -142,10 +145,10 @@ problem at all, depending on the implementation of the retry mechanism. So, this provides a way for drivers to avoid those error messages on calls where allocation failures are not a problem, and shouldn't bother the logs. -NOTE: At the moment DMA_ATTR_NO_WARN is only implemented on PowerPC. +.. note:: At the moment DMA_ATTR_NO_WARN is only implemented on PowerPC. DMA_ATTR_PRIVILEGED ------------------------------- +------------------- Some advanced peripherals such as remote processors and GPUs perform accesses to DMA buffers in both privileged "supervisor" and unprivileged |