i3c: Allow OF-alias-based persistent bus numbering

Parse the /aliases node to assign any fixed bus numbers, as is done with
the i2c subsystem. Numbering for non-aliased busses will start after the
highest fixed bus number.

This allows an alias node such as:

    aliases {
        i3c0 = &bus_a,
	i3c4 = &bus_b,
    };

to set the numbering for a set of i3c controllers:

    /* fixed-numbered bus, assigned "i3c-0" */
    bus_a: i3c-master {
    };

    /* another fixed-numbered bus, assigned "i3c-4" */
    bus_b: i3c-master {
    };

    /* dynamic-numbered bus, likely assigned "i3c-5" */
    bus_c: i3c-master {
    };

If no i3c device aliases are present, the numbering will stay as-is,
starting from 0.
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20230405094149.1513209-1-jk@codeconstruct.com.auSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/i3c/master.c

@@ -21,6 +21,7 @@
 
 static DEFINE_IDR(i3c_bus_idr);
 static DEFINE_MUTEX(i3c_core_lock);
+static int __i3c_first_dynamic_bus_num;
 
 /**
  * i3c_bus_maintenance_lock - Lock the bus for a maintenance operation
@@ -419,9 +420,9 @@ static void i3c_bus_cleanup(struct i3c_bus *i3cbus)
 	mutex_unlock(&i3c_core_lock);
 }
 
-static int i3c_bus_init(struct i3c_bus *i3cbus)
+static int i3c_bus_init(struct i3c_bus *i3cbus, struct device_node *np)
 {
-	int ret;
+	int ret, start, end, id = -1;
 
 	init_rwsem(&i3cbus->lock);
 	INIT_LIST_HEAD(&i3cbus->devs.i2c);
@@ -429,8 +430,19 @@ static int i3c_bus_init(struct i3c_bus *i3cbus)
 	i3c_bus_init_addrslots(i3cbus);
 	i3cbus->mode = I3C_BUS_MODE_PURE;
 
+	if (np)
+		id = of_alias_get_id(np, "i3c");
+
 	mutex_lock(&i3c_core_lock);
-	ret = idr_alloc(&i3c_bus_idr, i3cbus, 0, 0, GFP_KERNEL);
+	if (id >= 0) {
+		start = id;
+		end = start + 1;
+	} else {
+		start = __i3c_first_dynamic_bus_num;
+		end = 0;
+	}
+
+	ret = idr_alloc(&i3c_bus_idr, i3cbus, start, end, GFP_KERNEL);
 	mutex_unlock(&i3c_core_lock);
 
 	if (ret < 0)
@@ -2606,7 +2618,7 @@ int i3c_master_register(struct i3c_master_controller *master,
 	INIT_LIST_HEAD(&master->boardinfo.i2c);
 	INIT_LIST_HEAD(&master->boardinfo.i3c);
 
-	ret = i3c_bus_init(i3cbus);
+	ret = i3c_bus_init(i3cbus, master->dev.of_node);
 	if (ret)
 		return ret;
 
@@ -2830,8 +2842,16 @@ void i3c_dev_free_ibi_locked(struct i3c_dev_desc *dev)
 
 static int __init i3c_init(void)
 {
-	int res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);
+	int res;
+
+	res = of_alias_get_highest_id("i3c");
+	if (res >= 0) {
+		mutex_lock(&i3c_core_lock);
+		__i3c_first_dynamic_bus_num = res + 1;
+		mutex_unlock(&i3c_core_lock);
+	}
 
+	res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);
 	if (res)
 		return res;