[i2c] [patch 2.6.20-rc2] migration aids for i2c_adapter.dev removal

[David Brownell]

Hi Jean,

Based on our discussion which culminated in

  http://lists.lm-sensors.org/pipermail/i2c/2006-December/000648.html

see the appended patch, which I understand should be a 2.6.20 candidate.
You were particularly concerned about the class attribute, but it seemed
to me the other two changes would make it easier to get adapter driver
updates integrated sooner.

So I think the status of those discussions is summarized as:

 - four patches mostly switching diagnostics to i2c_adapter.class_dev.dev
   ... ready "now" for merge into MM

 - your patch initializing i2c_adapter.dev.parent for many adapters
   ... can merge at any time, though I'd suggest making them init
   i2c_adapter.class_dev.dev "now" (after merging the appended patch)
   rather than later;

 - my "patch #5/6" -- "5A" (without removal of i2c_adapter.dev from i2c-core)
   ... as above, can merge at any time after merging the appended patch

 - my "patch #5/6" -- "5B" (only the removal of i2c_adapter.dev)
   ... defer till july-ish

 - my "patch #6/6" (adding suspend/resume/shutdown methods)
   ... you didn't re-review, but should be ok at any time (after reissue
   to cope with #5B being deferred.  (And actually nice for 2.6.20 too.)

I'm not going to re-send the first four, unless you ask.  But after I send
this one, I'll send the revised #5A, and later #6; thinking those could go
into MM at any time after the appended patch.

Comments?

- Dave

================	CUT HERE
Flag i2c_adapter.dev for removal after userspace tools get upgraded, and
include some near-term code migration aids to facilitate this:

 - The class device gets the name attribute it should have had.  This
   was previously (wrongly) associated with the i2c_adapter.dev node.
   Sysfs tools can start converting right away.

 - Handle adapter drivers that have stopped using i2c_adapter.dev; init
   uses i2c_adapter.class_dev.dev if i2c_adapter.dev.parent is null.
   Adapter drivers can start converting right away.

 - Issue a warning for legacy adapter drivers that don't provide any
   physical device node, in either class_dev.dev or dev.parent; so
   systems with those drivers will know to fix this problem earlier.

This is one of a series of patches to help the I2C stack become a better
citizen of the Linux Driver Model world.

Signed-off-by: David Brownell <dbrownell at users.sourceforge.net>

Index: at91/Documentation/feature-removal-schedule.txt
===================================================================
--- at91.orig/Documentation/feature-removal-schedule.txt	2006-12-15 10:08:52.000000000 -0800
+++ at91/Documentation/feature-removal-schedule.txt	2006-12-28 17:03:18.000000000 -0800
@@ -226,6 +226,23 @@ Who:	Jean Delvare <khali at linux-fr.org>
 
 ---------------------------
 
+What:	i2c_adapter.dev
+	i2c_adapter.list
+When:	July 2007
+Why:	Superfluous, given i2c_adapter.class_dev:
+	  * The "dev" was a stand-in for the physical device node that legacy
+	    drivers would not have; but now it's almost always present.  Any
+	    remaining legacy drivers must upgrade (they now trigger warnings).
+	  * The "list" duplicates class device children.
+	The delay in removing this is so upgraded lm_sensors and libsensors
+	can get deployed.  (Removal causes minor changes in the sysfs layout,
+	notably the location of the adapter type name and parenting the i2c
+	client hardware directly from their controller.) 
+Who:	Jean Delvare <khali at linux-fr.org>,
+	David Brownell <dbrownell at users.sourceforge.net>
+
+---------------------------
+
 What:	IPv4 only connection tracking/NAT/helpers
 When:	2.6.22
 Why:	The new layer 3 independant connection tracking replaces the old
Index: at91/drivers/i2c/i2c-core.c
===================================================================
--- at91.orig/drivers/i2c/i2c-core.c	2006-12-28 16:21:07.000000000 -0800
+++ at91/drivers/i2c/i2c-core.c	2006-12-28 19:56:52.000000000 -0800
@@ -95,16 +95,32 @@ struct device_driver i2c_adapter_driver 
 	.bus = &i2c_bus_type,
 };
 
+/* ------------------------------------------------------------------------- */
+
+/* I2C bus adapters -- one roots each I2C or SMBUS segment */
+
 static void i2c_adapter_class_dev_release(struct class_device *dev)
 {
 	struct i2c_adapter *adap = class_dev_to_i2c_adapter(dev);
 	complete(&adap->class_dev_released);
 }
 
+static ssize_t i2c_adapter_show_name(struct class_device *cdev, char *buf)
+{
+	struct i2c_adapter *adap = class_dev_to_i2c_adapter(cdev);
+	return sprintf(buf, "%s\n", adap->name);
+}
+
+static struct class_device_attribute i2c_adapter_attrs[] = {
+	__ATTR(name, S_IRUGO, i2c_adapter_show_name, NULL),
+	{ },
+};
+
 struct class i2c_adapter_class = {
-	.owner =	THIS_MODULE,
-	.name =		"i2c-adapter",
-	.release =	&i2c_adapter_class_dev_release,
+	.owner =		THIS_MODULE,
+	.name =			"i2c-adapter",
+	.class_dev_attrs =	i2c_adapter_attrs,
+	.release =		&i2c_adapter_class_dev_release,
 };
 
 static ssize_t show_adapter_name(struct device *dev, struct device_attribute *attr, char *buf)
@@ -171,12 +187,21 @@ int i2c_add_adapter(struct i2c_adapter *
 	list_add_tail(&adap->list,&adapters);
 	INIT_LIST_HEAD(&adap->clients);
 
+	/* When we get rid of adap->dev, class_dev.dev must always be
+	 * provided.  Allow that init scheme before it's needed, too.
+	 */
+	if (adap->dev.parent == NULL)
+		adap->dev.parent = adap->class_dev.dev;
+
 	/* Add the adapter to the driver core.
 	 * If the parent pointer is not set up,
 	 * we add this adapter to the host bus.
 	 */
-	if (adap->dev.parent == NULL)
+	if (adap->dev.parent == NULL) {
 		adap->dev.parent = &platform_bus;
+		printk(KERN_WARNING "i2c-%d: physical device not specified\n",
+			adap->nr);
+	}
 	sprintf(adap->dev.bus_id, "i2c-%d", adap->nr);
 	adap->dev.driver = &i2c_adapter_driver;
 	adap->dev.release = &i2c_adapter_dev_release;