9 Feb
2021
9 Feb
'21
3:50 p.m.
On Tue, Feb 09, 2021 at 12:45:11PM +0000, Robin Murphy wrote:
It's not a bug, it's a fundamental design failure. dma_get_sgtable() has only ever sort-of-worked for DMA buffers that come from CMA or regular page allocations. In particular, a "no-map" DMA pool is not backed by kernel memory, so does not have any corresponding page structs, so it's impossible to generate a *valid* scatterlist to represent memory from that pool, regardless of what you might get away with provided you don't poke too hard at it.
It is not a good API...
Yes, I don't think anyone should add new users of the API.
That being said the commit he is trying to backport fixes a bug in the implementation that at least in theory could also affect in-tree drivers.