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SubjectRe: [PATCH v9 10/10] drivers/block/pmem: Map NVDIMM with ioremap_wt()
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On Thu, 2015-05-14 at 14:52 -0700, Dan Williams wrote:
> On Wed, May 13, 2015 at 2:05 PM, Toshi Kani <toshi.kani@hp.com> wrote:
> > The pmem driver maps NVDIMM with ioremap_nocache() as we cannot
> > write back the contents of the CPU caches in case of a crash.
> >
> > This patch changes to use ioremap_wt(), which provides uncached
> > writes but cached reads, for improving read performance.
>
> I'm thinking that for the libnd integration we don't want the pmem
> driver hard coding the cache-policy decision. This is something that
> should be specified to nd_pmem_region_create(). Especially
> considering that platform firmware tables (NFIT) may specify the cache
> policy for the range. As Matthew Wilcox mentioned offline we also
> must match the DAX-to-mmap cache policy with the policy for the driver
> mapping for architectures that are not capable of multiple mappings
> of the same physical address with different policies.

Agreed. I believe this hardcoded ioremap is temporary (either UC- or
WT), and we need to allow NFIT or user to specify a map type, such as
WB.

Thanks,
-Toshi



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