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由 Luis R. Rodriguez 提交于
We currently have no safe way of currently defining architecture agnostic IOMMU ioremap_*() variants. The trend is for folks to *assume* that ioremap_nocache() should be the default everywhere and then add this mapping on each architectures -- this is not correct today for a variety of reasons. We have two options: 1) Sit and wait for every architecture in Linux to get a an ioremap_*() variant defined before including it upstream. 2) Gather consensus on a safe architecture agnostic ioremap_*() default. Approach 1) introduces development latencies, and since 2) will take time and work on clarifying semantics the only remaining sensible thing to do to avoid issues is returning NULL on ioremap_*() variants. In order for this to work we must have all architectures declare their own ioremap_*() variants as defined. This will take some work, do this for ioremp_uc() to set the example as its only currently implemented on x86. Document all this. We only provide implementation support for ioremap_uc() as the other ioremap_*() variants are well defined all over the kernel for other architectures already. Signed-off-by: NLuis R. Rodriguez <mcgrof@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: arnd@arndb.de Cc: benh@kernel.crashing.org Cc: bp@suse.de Cc: dan.j.williams@intel.com Cc: geert@linux-m68k.org Cc: hch@lst.de Cc: hmh@hmh.eng.br Cc: jgross@suse.com Cc: linux-mm@kvack.org Cc: luto@amacapital.net Cc: mpe@ellerman.id.au Cc: mst@redhat.com Cc: ralf@linux-mips.org Cc: ross.zwisler@linux.intel.com Cc: stefan.bader@canonical.com Cc: tj@kernel.org Cc: tomi.valkeinen@ti.com Cc: toshi.kani@hp.com Link: http://lkml.kernel.org/r/1436488096-3165-1-git-send-email-mcgrof@do-not-panic.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
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