Re: [Linux-nvdimm] [PATCH 1/3] pmem: Initial version of persistent memory driver

[Ross Zwisler]

On Thu, 2015-03-26 at 15:35 +0100, Christoph Hellwig wrote:
> On Thu, Mar 26, 2015 at 07:12:23AM -0700, Dan Williams wrote:
> > > +       struct resource *res_mem;
> > > +       int err;
> > > +
> > > +       res_mem = request_mem_region_exclusive(pmem->phys_addr, pmem->size,
> > > +                                              "pmem");
> > 
> > Isn't request_mem_region() enough?  i.e. it seems
> > request_mem_region_exclusive() assumes no DAX, at least in theory?
> 
> This is 1:1 from the patch Ross sent, but I've been wondering why
> request_mem_region_exclusive is used here.  All it does is setting the
> IORESOURCE_EXCLUSIVE flag, which prevents /dev/mem and sysfs from accessing
> the memory while the driver claims it. Besides pmem only a watchdog driver
> and e1000 make use of this flag, and there's various function related to
> it that are entirely unused.  It's a weird beast.

I don't have a compelling reason to use request_mem_region_exclusive()
over request_mem_region().  If the latter is cleaner I'm fine with the
change.

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