On Sun, Jul 26, 2015 at 10:12 PM, Christoph Hellwig <hch(a)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(a)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