From f8bcbe62acd0e1ce9004b83e98a4af87ae385dcf Mon Sep 17 00:00:00 2001 From: Robert Jarzmik Date: Sat, 8 Aug 2015 10:44:10 +0200 Subject: lib: scatterlist: add sg splitting function Sometimes a scatter-gather has to be split into several chunks, or sub scatter lists. This happens for example if a scatter list will be handled by multiple DMA channels, each one filling a part of it. A concrete example comes with the media V4L2 API, where the scatter list is allocated from userspace to hold an image, regardless of the knowledge of how many DMAs will fill it : - in a simple RGB565 case, one DMA will pump data from the camera ISP to memory - in the trickier YUV422 case, 3 DMAs will pump data from the camera ISP pipes, one for pipe Y, one for pipe U and one for pipe V For these cases, it is necessary to split the original scatter list into multiple scatter lists, which is the purpose of this patch. The guarantees that are required for this patch are : - the intersection of spans of any couple of resulting scatter lists is empty. - the union of spans of all resulting scatter lists is a subrange of the span of the original scatter list. - streaming DMA API operations (mapping, unmapping) should not happen both on both the resulting and the original scatter list. It's either the first or the later ones. - the caller is reponsible to call kfree() on the resulting scatterlists. Signed-off-by: Robert Jarzmik Signed-off-by: Jens Axboe --- lib/Kconfig | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'lib/Kconfig') diff --git a/lib/Kconfig b/lib/Kconfig index 3a2ef67db6c7..dc516164415a 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -521,6 +521,13 @@ config UCS2_STRING source "lib/fonts/Kconfig" +config SG_SPLIT + def_bool n + help + Provides a heler to split scatterlists into chunks, each chunk being a + scatterlist. This should be selected by a driver or an API which + whishes to split a scatterlist amongst multiple DMA channel. + # # sg chaining option # -- cgit v1.2.3-58-ga151