Re: [PATCH v9 10/10] drivers/block/pmem: Map NVDIMM with ioremap_wt()

[Toshi Kani]

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@xxxxxx> 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/