[PATCH 1/2] of: fix race when matching drivers

[Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>]

From: Milton Miller <miltonm-ogEGBHC/i9Y@public.gmane.org>

If two drivers are probing devices at the same time, both will write
their match table result to the dev->of_match cache at the same time.

Only write the result if the device matches.

In a thread titled "SBus devices sometimes detected, sometimes not",
Meelis reported his SBus hme was not detected about 50% of the time.
>From the debug suggested by Grant it was obvious another driver matched
some devices between the call to match the hme and the hme discovery
failling.

Reported-by: Meelis Roos <mroos-Y27EyoLml9s@public.gmane.org>
Signed-off-by: Milton Miller <miltonm-ogEGBHC/i9Y@public.gmane.org>
[grant.likely: modified to only call of_match_device() once]
Signed-off-by: Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>
---
 include/linux/of_device.h |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/of_device.h b/include/linux/of_device.h
index 8bfe6c1..b33d688 100644
--- a/include/linux/of_device.h
+++ b/include/linux/of_device.h
@@ -21,8 +21,12 @@ extern void of_device_make_bus_id(struct device *dev);
 static inline int of_driver_match_device(struct device *dev,
 					 const struct device_driver *drv)
 {
-	dev->of_match = of_match_device(drv->of_match_table, dev);
-	return dev->of_match != NULL;
+	const struct of_device_id *match;
+
+	match = of_match_device(drv->of_match_table, dev);
+	if (match)
+		dev->of_match = match;
+	return match != NULL;
 }
 
 extern struct platform_device *of_dev_get(struct platform_device *dev);