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

From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>,
	Jens Axboe <axboe@kernel.dk>,
	linux-nvdimm <linux-nvdimm@ml01.01.org>, X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [Linux-nvdimm] [PATCH 1/3] pmem: Initial version of persistent memory driver
Date: Thu, 26 Mar 2015 15:37:41 -0600	[thread overview]
Message-ID: <1427405861.29730.5.camel@theros.lm.intel.com> (raw)
In-Reply-To: <20150326143520.GB1557@lst.de>

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.