[PATCH 1/1 v3] drivers/nvme: default to 4k device page size

[keith.busch@intel.com (Keith Busch)]

On Tue, Nov 03, 2015@05:18:24AM -0800, Christoph Hellwig wrote:
> On Fri, Oct 30, 2015@02:35:11PM -0700, Nishanth Aravamudan wrote:
> > diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
> > index ccc0c1f93daa..a9a5285bdb39 100644
> > --- a/drivers/block/nvme-core.c
> > +++ b/drivers/block/nvme-core.c
> > @@ -1717,7 +1717,12 @@ static int nvme_configure_admin_queue(struct nvme_dev *dev)
> >  	u32 aqa;
> >  	u64 cap = readq(&dev->bar->cap);
> >  	struct nvme_queue *nvmeq;
> > -	unsigned page_shift = PAGE_SHIFT;
> > +	/*
> > +	 * default to a 4K page size, with the intention to update this
> > +	 * path in the future to accomodate architectures with differing
> > +	 * kernel and IO page sizes.
> > +	 */
> > +	unsigned page_shift = 12;
> >  	unsigned dev_page_min = NVME_CAP_MPSMIN(cap) + 12;
> >  	unsigned dev_page_max = NVME_CAP_MPSMAX(cap) + 12;
> 
> Looks good as a start.  Note that all the MPSMIN/MAX checking could
> be removed as NVMe devices must support 4k pages.

MAX can go, and while it's probably the case that all devices support 4k,
it's not a spec requirement, so we should keep the dev_page_min check.