[PATCH 2/3] soundwire: bus: allow device number to be unique at system level

[Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>]

From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>

The SoundWire specification allows the device number to be allocated
at will. When a system includes multiple SoundWire links, the device
number scope is limited to the link to which the device is attached.

However, for integration/debug it can be convenient to have a unique
device number across the system. This patch adds a 'dev_num_ida_min'
field at the bus level, which when set will be used to allocate an
IDA.

The allocation happens when a hardware device reports as ATTACHED. If
any error happens during the enumeration, the allocated IDA is not
freed - the device number will be reused if/when the device re-joins
the bus. The IDA is only freed when the Linux device is unregistered.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@xxxxxxxxxxxxxxx>
Reviewed-by: Rander Wang <rander.wang@xxxxxxxxx>
Signed-off-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
---
 drivers/soundwire/bus.c       | 23 +++++++++++++++++------
 include/linux/soundwire/sdw.h |  4 ++++
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 37638c20c804..8970f8560766 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -12,6 +12,7 @@
 #include "sysfs_local.h"
 
 static DEFINE_IDA(sdw_bus_ida);
+static DEFINE_IDA(sdw_peripheral_ida);
 
 static int sdw_get_id(struct sdw_bus *bus)
 {
@@ -157,9 +158,11 @@ static int sdw_delete_slave(struct device *dev, void *data)
 
 	mutex_lock(&bus->bus_lock);
 
-	if (slave->dev_num) /* clear dev_num if assigned */
+	if (slave->dev_num) { /* clear dev_num if assigned */
 		clear_bit(slave->dev_num, bus->assigned);
-
+		if (bus->dev_num_ida_min)
+			ida_free(&sdw_peripheral_ida, slave->dev_num);
+	}
 	list_del_init(&slave->node);
 	mutex_unlock(&bus->bus_lock);
 
@@ -639,10 +642,18 @@ static int sdw_get_device_num(struct sdw_slave *slave)
 {
 	int bit;
 
-	bit = find_first_zero_bit(slave->bus->assigned, SDW_MAX_DEVICES);
-	if (bit == SDW_MAX_DEVICES) {
-		bit = -ENODEV;
-		goto err;
+	if (slave->bus->dev_num_ida_min) {
+		bit = ida_alloc_range(&sdw_peripheral_ida,
+				      slave->bus->dev_num_ida_min, SDW_MAX_DEVICES,
+				      GFP_KERNEL);
+		if (bit < 0)
+			goto err;
+	} else {
+		bit = find_first_zero_bit(slave->bus->assigned, SDW_MAX_DEVICES);
+		if (bit == SDW_MAX_DEVICES) {
+			bit = -ENODEV;
+			goto err;
+		}
 	}
 
 	/*
diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index 39058c841469..a2b31d25ea27 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -889,6 +889,9 @@ struct sdw_master_ops {
  * meaningful if multi_link is set. If set to 1, hardware-based
  * synchronization will be used even if a stream only uses a single
  * SoundWire segment.
+ * @dev_num_ida_min: if set, defines the minimum values for the IDA
+ * used to allocate system-unique device numbers. This value needs to be
+ * identical across all SoundWire bus in the system.
  */
 struct sdw_bus {
 	struct device *dev;
@@ -913,6 +916,7 @@ struct sdw_bus {
 	u32 bank_switch_timeout;
 	bool multi_link;
 	int hw_sync_min_links;
+	int dev_num_ida_min;
 };
 
 int sdw_bus_master_add(struct sdw_bus *bus, struct device *parent,
-- 
2.25.1