[PATCH 05/14] init: deps: order I2C bus drivers by their ID

[Alexander Holler <holler@ahsoftware.de>]

In order to provide a stable I2C bus numbering, we order I2C bus drivers
according to their driver ID.

If that is better or worse than ordering by link order might have to be
discussed, but for now, it's good to provide an example about how to order
something based on driver IDs.

Signed-off-by: Alexander Holler <holler@ahsoftware.de>
---
 include/linux/driver_ids.h |  9 +++++++++
 init/dependencies.c        | 25 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/linux/driver_ids.h b/include/linux/driver_ids.h
index 1133a68..330080e 100644
--- a/include/linux/driver_ids.h
+++ b/include/linux/driver_ids.h
@@ -17,6 +17,15 @@ enum {
 	/* To be filled */
 
 	/*
+	 * I2C bus drivers will be ordered according to their ID (which
+	 * means according to their appearance here).
+	 * This provides stable I2C bus numbers.
+	 * Therefor their IDs have to be in the following block.
+	 */
+	drvid_i2c_busses_start,
+	drvid_i2c_busses_end,
+
+	/*
 	 * Network drivers will be ordered according to the link order
 	 * (which means not necessarily according to their appearance
 	 * here).
diff --git a/init/dependencies.c b/init/dependencies.c
index 027fc4b..d20d6fc 100644
--- a/init/dependencies.c
+++ b/init/dependencies.c
@@ -298,10 +298,22 @@ static int __init add_dependencies(void)
 	return 0;
 }
 
+static int __init compare_unsigned(const void *lhs, const void *rhs)
+{
+	if (*(unsigned *)lhs < *(unsigned *)rhs)
+		return -1;
+	if (*(unsigned *)lhs > *(unsigned *)rhs)
+		return 1;
+	return 0;
+}
+
 static void __init build_inventory(void)
 {
 	const struct _annotated_initcall *ac;
 	unsigned id_last_network_driver = 0;
+	unsigned id_i2c_bus_driver[drvid_i2c_busses_end
+				   - drvid_i2c_busses_start];
+	unsigned count_i2c_bus_drivers = 0;
 
 	ac = __annotated_initcall_start;
 	for (; ac < __annotated_initcall_end; ++ac) {
@@ -316,6 +328,19 @@ static void __init build_inventory(void)
 					id_last_network_driver);
 			id_last_network_driver = ac->id;
 		}
+		/* order I2C bus drivers by their ID */
+		if (ac->id > drvid_i2c_busses_start &&
+				ac->id < drvid_i2c_busses_end)
+			id_i2c_bus_driver[count_i2c_bus_drivers++] = ac->id;
+	}
+	if (count_i2c_bus_drivers > 1) {
+		unsigned i;
+
+		sort(id_i2c_bus_driver, count_i2c_bus_drivers,
+				sizeof(unsigned), &compare_unsigned, NULL);
+		for (i = 1; i < count_i2c_bus_drivers; ++i)
+			add_initcall_dependency(id_i2c_bus_driver[i],
+				id_i2c_bus_driver[i-1]);
 	}
 }
 
-- 
2.1.0