Messages in this thread | | | Date | Fri, 29 Apr 2011 17:42:59 +0100 | Subject | Re: [RFC] ARM DMA mapping TODO, v1 | From | Catalin Marinas <> |
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On Friday, 29 April 2011, Arnd Bergmann <arnd@arndb.de> wrote: > On Wednesday 27 April 2011, Catalin Marinas wrote: >> > > >> > > It's not broken since we moved to using Normal non-cacheable memory >> > > for the coherent DMA buffers (as long as you flush the cacheable alias >> > > before using the buffer, as we already do). The ARM ARM currently says >> > > unpredictable for such situations but this is being clarified in >> > > future updates and the Normal non-cacheable vs cacheable aliases can >> > > be used (given correct cache maintenance before using the buffer). >> > >> > Thanks for that information, I believe a number of people in the >> > previous discussions were relying on the information from the >> > documentation. Are you sure that this is not only correct for the >> > cores made by ARM ltd but also for the other implementations that >> > may have relied on documentation? >> >> It is a clarification in the ARM ARM so it covers all the cores made by >> architecture licensees, not just ARM Ltd. It basically makes the >> "unpredictable" part more predictable to allow certain types of aliases >> (e.g. Strongly Ordered vs Normal memory would still be disallowed). >> >> All the current implementations are safe with Normal memory aliases >> (cacheable vs non-cacheable) but of course, there may be some >> performance benefits in not having any alias. > > A lot of the discussions we are about to have in Budapest will be > around solving the problem of having only valid combinations of > mappings, so we really need to have a clear statement in specification > form about what is actually valid. > > Would it be possible to have an updated version of the relevant > section of the ARM ARM by next week so we can use that as the > base for our discussions?
I'll ask the architecture people here in ARM and get back to you (there is holiday until Tuesday next week in the UK).
-- Catalin
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