On 23 February 2016 at 13:03, Ard Biesheuvel <ard.biesheu...@linaro.org> wrote: > 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.
OK, I see what you mean. I find it unfortunate that ioremap_cache() instances are blindly being replaced with memremap(), and I wonder if this wasted test by and/or cc'ed to people who can actually test this driver. Dan? Anyway, I don't think it makes sense to stipulate at the generic level that ioremap_cache() and memremap(MEMREMAP_WB) shall be the same, and deprecating it is a bit premature since the cross-architecturally loosely defined semantics of ioremap_cache() can never be replaced 1:1 with what memremap() promises. So what I suggest is that I revert the change to pxa2xx-flash as a new 1/3 in this series, and put these existing two on top to decouple memremap(MEMREMAP_WB) from ioremap_cache() entirely. Thanks, Ard.