Thanks Stephen for explaining the background of this patch.

On Fri, 11 May 2012 00:34:40 +0200
Stephen Warren [off-list ref] wrote:

On 05/10/2012 04:28 PM, Greg Kroah-Hartman wrote:

quoted

On Thu, May 10, 2012 at 02:00:48PM -0600, Stephen Warren wrote:

quoted

On 05/10/2012 12:16 PM, Greg Kroah-Hartman wrote:

quoted

On Thu, May 10, 2012 at 09:59:15AM -0600, Stephen Warren wrote:

quoted

On 05/10/2012 08:11 AM, Greg Kroah-Hartman wrote:

quoted

On Thu, May 10, 2012 at 10:35:02AM +0300, Hiroshi DOYU wrote:

quoted

driver_find_device() can be called with an unregistered driver.

...

quoted

Can someone resend this to me, with the information above in the
changelog comment, and I'll be glad to apply it?  Again, I need to know
if this is needed for 3.4 or it can wait for 3.5?

I'll let Hiroshi do that.

Greg, here's the update patch with the above explanation. Please take
this one if the following explanation makes sense.

From d7cf9b53d3bbcce75ae55a9eed03c7e091529e3d Mon Sep 17 00:00:00 2001

From: Hiroshi DOYU <redacted>
Date: Wed, 9 May 2012 14:21:03 +0300
Subject: [PATCH 1/1] Driver Core: don't oops with unregistered driver in
 driver_find_device()

driver_find_device() can be called with an unregistered driver. Need
to check driver_private to see if it's populated or not, especially
under deferrable probe.

In the case that there are 2 drivers, one depends on the other. With
-EPROBE_DEFER, two drivers can use deferred probe to ensure that their
relative probe order doesn't matter. If dependee driver is probed
first, then the dependant's driver_find_device('dependee')
succeeds. If the dependant is probed first, then the dependant's
driver_find_device('dependee') should return NULL, and the dependant
should get -EPROBE_DEFER. driver_find_device() needs to return NULL if
it's not populated.

Signed-off-by: Hiroshi DOYU <redacted>
---
In [PATCHv5 2/3] ARM: tegra: Add SMMU enabler in AHB:
  http://article.gmane.org/gmane.linux.ports.tegra/4658

"tegra_ahb_driver" may not be populated when it's called.

For more SMMU/AHB specific discussion, refer to the following thread:
  https://lkml.org/lkml/2012/5/10/21
---
 drivers/base/driver.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 3ec3896..207c27d 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c

@@ -80,7 +80,7 @@ struct device *driver_find_device(struct device_driver *drv,
 	struct klist_iter i;
 	struct device *dev;
 
-	if (!drv)
+	if (!drv || !drv->p)
 		return NULL;
 
 	klist_iter_init_node(&drv->p->klist_devices, &i,

-- 
1.7.5.4