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. 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. 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. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
