linux-kernel - [PATCH] driver core: check bus->match without holding device lock

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Date:	Tue, 20 Jan 2009 21:34:08 +0800
From:	tom.leiming@...il.com
To:	kay.sievers@...y.org, greg@...ah.com
Cc:	linux-kernel@...r.kernel.org, arjan@...ux.intel.com,
	Ming Lei <tom.leiming@...il.com>
Subject: [PATCH] driver core: check bus->match without holding device lock

From: Ming Lei <tom.leiming@...il.com>

This patch moves bus->match out from driver_probe_device and
does not hold device lock to check the match between a device
and a driver.

The idea has been verified by the commit 6cd495860901,
which leads to a faster boot. But the commit 6cd495860901 has
the following drawbacks: 1),only does the quick check in
the path of __driver_attach->driver_probe_device, not in other
paths; 2),for a matched device and driver, check the same match
twice. It is a waste of cpu ,especially for some drivers with long
device id table (eg. usb-storage driver).

This patch adds a helper of driver_match_device to check the match
in all paths, and testes the match only once.

Signed-off-by: Ming Lei <tom.leiming@...il.com>
---
 drivers/base/bus.c     |    8 +++++++-
 drivers/base/dd.c      |   19 +++++++------------
 include/linux/device.h |    6 ++++++
 3 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 83f32b8..c570d16 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -199,6 +199,12 @@ static ssize_t driver_bind(struct device_driver *drv,
 
 	dev = bus_find_device_by_name(bus, NULL, buf);
 	if (dev && dev->driver == NULL) {
+
+		if (!driver_match_device(drv, dev)) {
+			err = 0;
+			goto not_match;
+		}
+
 		if (dev->parent)	/* Needed for USB */
 			down(&dev->parent->sem);
 		down(&dev->sem);
@@ -206,7 +212,7 @@ static ssize_t driver_bind(struct device_driver *drv,
 		up(&dev->sem);
 		if (dev->parent)
 			up(&dev->parent->sem);
-
+not_match:
 		if (err > 0) {
 			/* success */
 			err = count;
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 315bed8..61f32db 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -172,14 +172,8 @@ int driver_probe_done(void)
  * @drv: driver to bind a device to
  * @dev: device to try to bind to the driver
  *
- * First, we call the bus's match function, if one present, which should
- * compare the device IDs the driver supports with the device IDs of the
- * device. Note we don't do this ourselves because we don't know the
- * format of the ID structures, nor what is to be considered a match and
- * what is not.
- *
- * This function returns 1 if a match is found, -ENODEV if the device is
- * not registered, and 0 otherwise.
+ * This function returns -ENODEV if the device is not registered,
+ * and 0 otherwise.
  *
  * This function must be called with @dev->sem held.  When called for a
  * USB interface, @dev->parent->sem must be held as well.
@@ -190,21 +184,22 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
 
 	if (!device_is_registered(dev))
 		return -ENODEV;
-	if (drv->bus->match && !drv->bus->match(dev, drv))
-		goto done;
 
 	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
 		 drv->bus->name, __func__, dev_name(dev), drv->name);
 
 	ret = really_probe(dev, drv);
 
-done:
 	return ret;
 }
 
 static int __device_attach(struct device_driver *drv, void *data)
 {
 	struct device *dev = data;
+
+	if (!driver_match_device(drv, dev))
+		return 0;
+
 	return driver_probe_device(drv, dev);
 }
 
@@ -257,7 +252,7 @@ static int __driver_attach(struct device *dev, void *data)
 	 * is an error.
 	 */
 
-	if (drv->bus->match && !drv->bus->match(dev, drv))
+	if (!driver_match_device(drv, dev))
 		return 0;
 
 	if (dev->parent)	/* Needed for USB */
diff --git a/include/linux/device.h b/include/linux/device.h
index 45e5b19..3c61315 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -466,6 +466,12 @@ static inline int device_is_registered(struct device *dev)
 	return dev->kobj.state_in_sysfs;
 }
 
+static inline int driver_match_device(struct device_driver *drv,
+				      struct device *dev)
+{
+	return drv->bus->match && drv->bus->match(dev, drv);
+}
+
 void driver_init(void);
 
 /*
-- 
1.6.0

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