Re: [patch 2.6.24-rc5-git] add i2c_new_dummy() utility

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

This adds a i2c_new_dummy() primitive to help work with devices
that consume multiple addresses, which include many I2C eeproms
and at least one RTC.

Signed-off-by: David Brownell <dbrownell-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
---
Updated to match Jean's feedback.  Tested with 24c00 EEPROM,
which takes eight addresses (but stores only 16 bytes total).

 drivers/i2c/i2c-core.c |   60 ++++++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/i2c.h    |    6 ++++
 2 files changed, 65 insertions(+), 1 deletion(-)

--- a/drivers/i2c/i2c-core.c	2007-12-22 13:54:04.000000000 -0800
+++ b/drivers/i2c/i2c-core.c	2007-12-22 13:57:15.000000000 -0800
@@ -276,6 +276,51 @@ void i2c_unregister_device(struct i2c_cl
 EXPORT_SYMBOL_GPL(i2c_unregister_device);
 
 
+static int dummy_nop(struct i2c_client *client)
+{
+	return 0;
+}
+
+static struct i2c_driver dummy_driver = {
+	.driver.name	= "dummy",
+	.probe		= dummy_nop,
+	.remove		= dummy_nop,
+};
+
+
+/**
+ * i2c_new_dummy - return a new i2c device bound to a dummy driver
+ * @adapter: the adapter managing the device
+ * @address: seven bit address to be used
+ * @type: optional label used for i2c_client.name
+ * Context: can sleep
+ *
+ * This returns an I2C client bound to the "dummy" driver, intended for use
+ * with devices that consume multiple addresses.  Examples of such chips
+ * include various EEPROMS (like 24c04 and 24c08 models).
+ *
+ * These dummy devices have two main uses.  First, most I2C and SMBus calls
+ * except i2c_transfer() need a client handle; the dummy will be that handle.
+ * And second, this prevents the specified address from being bound to a
+ * different driver.
+ *
+ * This returns the new i2c client, which should be saved for later use with
+ * i2c_unregister_device(); or NULL to indicate an error.
+ */
+struct i2c_client *
+i2c_new_dummy(struct i2c_adapter *adapter, u16 address, const char *type)
+{
+	struct i2c_board_info info = {
+		.driver_name	= "dummy",
+		.addr		= address,
+	};
+
+	if (type)
+		strlcpy(info.type, type, sizeof info.type);
+	return i2c_new_device(adapter, &info);
+}
+EXPORT_SYMBOL_GPL(i2c_new_dummy);
+
 /* ------------------------------------------------------------------------- */
 
 /* I2C bus adapters -- one roots each I2C or SMBUS segment */
@@ -848,11 +893,24 @@ static int __init i2c_init(void)
 	retval = bus_register(&i2c_bus_type);
 	if (retval)
 		return retval;
-	return class_register(&i2c_adapter_class);
+	retval = class_register(&i2c_adapter_class);
+	if (retval)
+		goto bus_err;
+	retval = i2c_add_driver(&dummy_driver);
+	if (retval)
+		goto class_err;
+	return 0;
+
+class_err:
+	class_unregister(&i2c_adapter_class);
+bus_err:
+	bus_unregister(&i2c_bus_type);
+	return retval;
 }
 
 static void __exit i2c_exit(void)
 {
+	i2c_del_driver(&dummy_driver);
 	class_unregister(&i2c_adapter_class);
 	bus_unregister(&i2c_bus_type);
 }
--- a/include/linux/i2c.h	2007-12-22 13:54:04.000000000 -0800
+++ b/include/linux/i2c.h	2007-12-22 13:57:15.000000000 -0800
@@ -261,6 +261,12 @@ i2c_new_probed_device(struct i2c_adapter
 		      struct i2c_board_info *info,
 		      unsigned short const *addr_list);
 
+/* For devices that use several addresses, use i2c_new_dummy() to make
+ * client handles for the extra addresses.
+ */
+extern struct i2c_client *
+i2c_new_dummy(struct i2c_adapter *adap, u16 address, const char *type);
+
 extern void i2c_unregister_device(struct i2c_client *);
 
 /* Mainboard arch_initcall() code should register all its I2C devices.