Date:	Sun, 3 Sep 2006 18:23:05 -0700
From:	David Brownell <david-b@...bell.net>
To:	linux-kernel@...r.kernel.org
Cc:	Russell King <rmk@....linux.org.uk>, Greg KH <greg@...ah.com>
Subject: [patch/RFC 2.6.18-rc] platform_device_probe(), to conserve memory

This defines a new platform_driver_probe() method allowing the driver's
probe() method, and its support code+data, to safely live in __init
sections for common system configurations.

Many system-on-chip processors could benefit from this API to the tune
of saving hundreds to thousands of bytes per driver, which is currently
wasted holding code which can never be called after system startup yet may
not be removed.   It may not be removed because of the linkage requirement
that pointers to init section code (like, ideally, probe support) must
not live in sections that persist after that section is removed (like
driver methods) when those pointers would be invalid.

Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>

Index: g26/include/linux/platform_device.h
===================================================================
--- g26.orig/include/linux/platform_device.h	2006-09-03 13:02:23.000000000 -0700
+++ g26/include/linux/platform_device.h	2006-09-03 13:02:49.000000000 -0700
@@ -58,6 +58,12 @@ struct platform_driver {
 extern int platform_driver_register(struct platform_driver *);
 extern void platform_driver_unregister(struct platform_driver *);
 
+/* non-hotpluggable platform devices may use this so that probe() and
+ * its support may live in __init sections, conserving runtime memory.
+ */
+extern int platform_driver_probe(struct platform_driver *driver,
+		int (*probe)(struct platform_device *));
+
 #define platform_get_drvdata(_dev)	dev_get_drvdata(&(_dev)->dev)
 #define platform_set_drvdata(_dev,data)	dev_set_drvdata(&(_dev)->dev, (data))
 
Index: g26/drivers/base/platform.c
===================================================================
--- g26.orig/drivers/base/platform.c	2006-09-03 13:02:23.000000000 -0700
+++ g26/drivers/base/platform.c	2006-09-03 13:02:49.000000000 -0700
@@ -451,6 +451,51 @@ void platform_driver_unregister(struct p
 }
 EXPORT_SYMBOL_GPL(platform_driver_unregister);
 
+/**
+ * platform_driver_probe - register driver for non-hotpluggable device
+ * @drv: platform driver structure
+ * @probe: the driver probe routine, probably from an __init section
+ *
+ * Use this instead of platform_driver_register() when you know the device
+ * is not hotpluggable and has already been registered, and you want to
+ * remove its run-once probe() infrastructure from memory after the driver
+ * has bound to the device.
+ *
+ * One typical use for this would be with drivers for controllers integrated
+ * into system-on-chip processors, where the controller devices have been
+ * configured as part of board setup.
+ *
+ * Returns zero if the driver registered and bound to a device, else returns
+ * a negative error code and with the driver not registered.
+ */
+int platform_driver_probe(struct platform_driver *drv,
+		int (*probe)(struct platform_device *))
+{
+	int retval;
+
+	/* temporary section violation */
+	drv->probe = probe;
+
+	retval = platform_driver_register(drv);
+	if (retval)
+		return retval;
+
+	/* Fixup that section violation, being paranoid about code scanning
+	 * the list of drivers in order to probe new devices.  Check to see
+	 * if the probe was successful.
+	 */
+	spin_lock(&platform_bus_type.klist_drivers.k_lock);
+	drv->driver.probe = NULL;
+	drv->probe = NULL;
+	if (list_empty(&drv->driver.klist_devices.k_list))
+		retval = -ENODEV;
+	spin_unlock(&platform_bus_type.klist_drivers.k_lock);
+
+	if (retval)
+		platform_driver_unregister(drv);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(platform_driver_probe);
 
 /* modalias support enables more hands-off userspace setup:
  * (a) environment variable lets new-style hotplug events work once system is

-- 
VGER BF report: U 0.499965
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