• Luis R. Rodriguez's avatar
    x86/mm, asm-generic: Add IOMMU ioremap_uc() variant default · 8c7ea50c
    Luis R. Rodriguez authored
    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: default avatarLuis 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: default avatarIngo Molnar <mingo@kernel.org>
    8c7ea50c
io.h 18.3 KB