[PATCH 4/9] dax/kmem: allow PMEM devices to bind to KMEM driver

[Dave Hansen]

Currently, a persistent memory device's mode must be coordinated
with the driver to which it needs to bind.  To change it from the
fsdax to the device-dax driver, you first change the mode of the
device itself.

Instead of adding a new device mode, allow the PMEM mode to also
bind to the KMEM driver.

As I write this, I'm realizing that it might have just been
better to add a new device mode, rather than hijacking the PMEM
eode.  If this is the case, please speak up, NVDIMM folks.  :)

Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: linux-nvdimm@xxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>

---

 b/drivers/nvdimm/bus.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff -puN drivers/nvdimm/bus.c~dax-kmem-try-again-2018-3-bus-match-override drivers/nvdimm/bus.c
--- a/drivers/nvdimm/bus.c~dax-kmem-try-again-2018-3-bus-match-override	2018-10-22 13:12:22.522930391 -0700
+++ b/drivers/nvdimm/bus.c	2018-10-22 13:12:22.525930391 -0700
@@ -464,11 +464,24 @@ static struct nd_device_driver nd_bus_dr
 static int nvdimm_bus_match(struct device *dev, struct device_driver *drv)
 {
 	struct nd_device_driver *nd_drv = to_nd_device_driver(drv);
+	bool match;
 
 	if (is_nvdimm_bus(dev) && nd_drv == &nd_bus_driver)
 		return true;
 
-	return !!test_bit(to_nd_device_type(dev), &nd_drv->type);
+	match = !!test_bit(to_nd_device_type(dev), &nd_drv->type);
+
+	/*
+	 * We allow PMEM devices to be bound to the KMEM driver.
+	 * Force a match if we detect a PMEM device type but
+	 * a KMEM device driver.
+	 */
+	if (!match &&
+	    (to_nd_device_type(dev) == ND_DEVICE_DAX_PMEM) &&
+	    (nd_drv->type == ND_DRIVER_DAX_KMEM))
+		match = true;
+
+	return match;
 }
 
 static ASYNC_DOMAIN_EXCLUSIVE(nd_async_domain);
_