[RFC PATCH] platform: Faciliatate the creation of pseduo-platformbusses

[Patrick Pannuto]

Inspiration for this comes from:
http://www.mail-archive.com/linux-omap@xxxxxxxxxxxxxxx/msg31161.html

INTRO

As SOCs become more popular, the desire to quickly define a simple,
but functional, bus type with only a few unique properties becomes
desirable. As they become more complicated, the ability to nest these
simple busses and otherwise orchestrate them to match the actual
topology also becomes desirable.

EXAMPLE USAGE

/arch/ARCH/MY_ARCH/my_bus.c:

	#include <linux/device.h>
	#include <linux/platform_device.h>

	struct bus_type my_bus_type = {
		.name	= "mybus",
	};
	EXPORT_SYMBOL_GPL(my_bus_type);

	struct platform_device sub_bus1 = {
		.name		= "sub_bus1",
		.id		= -1,
		.dev.bus	= &my_bus_type,
	}
	EXPORT_SYMBOL_GPL(sub_bus1);

	struct platform_device sub_bus2 = {
		.name		= "sub_bus2",
		.id		= -1,
		.dev.bus	= &my_bus_type,
	}
	EXPORT_SYMBOL_GPL(sub_bus2);

	static int __init my_bus_init(void)
	{
		int error;
		platform_bus_type_init(&my_bus_type);

		error = bus_register(&my_bus_type);
		if (error)
			return error;

		error = platform_device_register(&sub_bus1);
		if (error)
			goto fail_sub_bus1;

		error = platform_device_register(&sub_bus2);
		if (error)
			goto fail_sub_bus2;

		return error;

	fail_sub_bus2:
		platform_device_unregister(&sub_bus1);
	fail_sub_bus2:
		bus_unregister(&my_bus_type);

		return error;
	}
	postcore_initcall(my_bus_init);
	EXPORT_SYMBOL_CPY(my_bus_init);

/drivers/my_driver.c
	static struct platform_driver my_driver = {
		.driver	= {
			.name	= "my-driver",
			.owner	= THIS_MODULE,
			.bus	= &my_bus_type,
		},
	};

/somewhere/my_device.c
	static struct platform_device my_device = {
		.name		= "my-device",
		.id		= -1,
		.dev.bus	= &my_bus_type,
		.dev.parent	= &sub_bus_1.dev,
	};

Notice that for a device / driver, only 3 lines were added to
switch from the platform bus to the new my_bus. This is
especially valuable if we consider supporting a legacy SOCs
and new SOCs where the same driver is used, but may need to
be on either the platform bus or the new my_bus. The above
code then becomes:

	(possibly in a header)
	#ifdef CONFIG_MY_BUS
	#define MY_BUS_TYPE	&my_bus_type
	#else
	#define MY_BUS_TYPE	NULL
	#endif

/drivers/my_driver.c
	static struct platform_driver my_driver = {
		.driver	= {
			.name	= "my-driver",
			.owner	= THIS_MODULE,
			.bus	= MY_BUS_TYPE,
		},
	};

Which will allow the same driver to easily to used on either
the platform bus or the newly defined bus type.

This will build a device tree that mirrors the actual configuration:
    /sys/bus
    |-- my_bus
    |   |-- devices
    |   |   |-- sub_bus1 -> ../../../devices/platform/sub_bus1
    |   |   |-- sub_bus2 -> ../../../devices/platform/sub_bus2
    |   |   |-- my-device -> ../../../devices/platform/sub_bus1/my-device
    |   |-- drivers
    |   |   |-- my-driver

I believe this to be a fairly elegant and simple solution to the
problem, but humbly RFC

-Pat

Signed-off-by: Patrick Pannuto <ppannuto@xxxxxxxxxxxxxx>
---
 drivers/base/platform.c         |   30 ++++++++++++++++++++++++++----
 include/linux/platform_device.h |    2 ++
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 4d99c8b..c86be03 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -241,7 +241,8 @@ int platform_device_add(struct platform_device *pdev)
 	if (!pdev->dev.parent)
 		pdev->dev.parent = &platform_bus;
 
-	pdev->dev.bus = &platform_bus_type;
+	if (!pdev->dev.bus)
+		pdev->dev.bus = &platform_bus_type;
 
 	if (pdev->id != -1)
 		dev_set_name(&pdev->dev, "%s.%d", pdev->name,  pdev->id);
@@ -482,7 +483,8 @@ static void platform_drv_shutdown(struct device *_dev)
  */
 int platform_driver_register(struct platform_driver *drv)
 {
-	drv->driver.bus = &platform_bus_type;
+	if (!drv->driver.bus)
+		drv->driver.bus = &platform_bus_type;
 	if (drv->probe)
 		drv->driver.probe = platform_drv_probe;
 	if (drv->remove)
@@ -539,12 +541,12 @@ int __init_or_module platform_driver_probe(struct platform_driver *drv,
 	 * if the probe was successful, and make sure any forced probes of
 	 * new devices fail.
 	 */
-	spin_lock(&platform_bus_type.p->klist_drivers.k_lock);
+	spin_lock(&drv->driver.bus->p->klist_drivers.k_lock);
 	drv->probe = NULL;
 	if (code == 0 && list_empty(&drv->driver.p->klist_devices.k_list))
 		retval = -ENODEV;
 	drv->driver.probe = platform_drv_probe_fail;
-	spin_unlock(&platform_bus_type.p->klist_drivers.k_lock);
+	spin_unlock(&drv->driver.bus->p->klist_drivers.k_lock);
 
 	if (code != retval)
 		platform_driver_unregister(drv);
@@ -1017,6 +1019,26 @@ struct bus_type platform_bus_type = {
 };
 EXPORT_SYMBOL_GPL(platform_bus_type);
 
+/** platform_bus_type_init - fill in a pseudo-platform-bus
+  * @bus: foriegn bus type
+  *
+  * This init is basically a selective memcpy that
+  * won't overwrite any user-defined attributes and
+  * only copies things that platform bus defines anyway
+  */
+void platform_bus_type_init(struct bus_type *bus)
+{
+	if (!bus->dev_attrs)
+		bus->dev_attrs = platform_bus_type.dev_attrs;
+	if (!bus->match)
+		bus->match = platform_bus_type.match;
+	if (!bus->uevent)
+		bus->uevent = platform_bus_type.uevent;
+	if (!bus->pm)
+		bus->pm = platform_bus_type.pm;
+}
+EXPORT_SYMBOL_GPL(platform_bus_type_init);
+
 int __init platform_bus_init(void)
 {
 	int error;
diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
index 5417944..fa8c35a 100644
--- a/include/linux/platform_device.h
+++ b/include/linux/platform_device.h
@@ -79,6 +79,8 @@ extern int platform_driver_probe(struct platform_driver *driver,
 #define platform_get_drvdata(_dev)	dev_get_drvdata(&(_dev)->dev)
 #define platform_set_drvdata(_dev,data)	dev_set_drvdata(&(_dev)->dev, (data))
 
+extern void platform_bus_type_init(struct bus_type *);
+
 extern struct platform_device *platform_create_bundle(struct platform_driver *driver,
 					int (*probe)(struct platform_device *),
 					struct resource *res, unsigned int n_res,
-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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