[PATCH v2 08/25] arch: introduce memremap()

[Dan Williams]

On Sun, Jul 26, 2015 at 10:12 PM, Christoph Hellwig <hch at lst.de> wrote:
> On Sun, Jul 26, 2015 at 10:49:39AM -0700, Dan Williams wrote:
>> On Sun, Jul 26, 2015 at 10:25 AM, Christoph Hellwig <hch at lst.de> wrote:
>> > On Fri, Jul 24, 2015 at 10:38:42PM -0400, Dan Williams wrote:
>> >> The behavior change to return NULL on an unsupported request is reserved
>> >> for a later patch.
>> >
>> > Why?
>>
>> This is for drivers like pmem that care about the mapping type.  For
>> example, if pmem can't get a cache-enabled mapping it is potentially
>> putting the write durability of the persistent media at risk.
>
> I understand that part, but the question is why the old behavior
> is retained for now and only changed later.

Oh, because all we have at this point is ioremap_cache() which
silently falls back.  It's not until the introduction of
arch_memremp() where we update the arch code to break that behavior.

That said, I think it may be beneficial to allow a fallback if the
user cares.  So maybe memremap() can call plain ioremap() if
MEMREMAP_STRICT is not set and none of the other mapping types are
satisfied.