On 23 February 2016 at 12:58, Russell King - ARM Linux <li...@arm.linux.org.uk> wrote: > On Mon, Feb 22, 2016 at 09:35:24PM +0100, Ard Biesheuvel wrote: >> OK, thanks for the historical context. >> >> So what is your opinion on this series, i.e., to wire up memremap() to >> remap arbitrary memory regions into the vmalloc area with MT_MEMORY_RW >> attributes, and at the same time lift the restriction that the region >> must be disjoint from memory covered by lowmem or kmap? > > The historical context is still present, because pxa2xx-flash has > been converted to use memremap() from ioremap_cache() - possibly > inappropriately. > > I've already described the semantics of ioremap_cache(), which are > to always create a cacheable mapping irrespective of the system > memory mapping type. However, memremap() says that MEMREMAP_WB > matches system RAM, which on ARM it doesn't right now. >
Indeed. Hence this series, to decouple memremap(MEMREMAP_WB) from ioremap_cache() for ARM > Changing it to MT_MEMORY_RW would satisfy that comment against > memremap(), but at the same time changes what happens with > pxa2xx-flash - the memory region (which is not system RAM) then > changes with the cache status of system RAM. > > So, I'm not that happy about the memremap() stuff right now, and > I don't like the idea of making memremap() conform to its stated > requirements without first preventing pxa2xx-flash being affected > by such a change. > Actually, my change fixes this issue, since it will cause memremap() to always create MT_MEMORY_RW mappings, and not fallback to ioremap_cache() for ranges that are not covered by lowmem. > Perhaps we need to reinstate the original ioremap_cached() API for > pxa2xx-flash, and then switch memremap() to MT_MEMORY_RW - that > would seem to result in the expected behaviour by all parties. > I think we can simply revert the change to pxa2xx-flash if it is deemed inappropriate.