[PATCH 4/8] i3c: master: Ensure Hot-Join operations are stopped on shutdown

[Adrian Hunter <adrian.hunter@intel.com>]

System shutdown invokes each device's bus shutdown callback to quiesce
hardware, but the I3C bus type does not currently implement one.  As a
result, on shutdown the controller's Hot-Join work and any in-flight
i3c_master_do_daa() can keep running (or be newly triggered) while the
rest of the system is being torn down.

A similar window exists at i3c_master_unregister() time: cancel_work_sync()
on hj_work prevents queued work from completing, but does not stop a
fresh Hot-Join IBI from re-queueing the worker, nor a concurrent sysfs
writer from toggling Hot-Join via i3c_set_hotjoin().

Introduce a single "shutting down" gate in the I3C core, set under the
bus maintenance lock so it is observed by any in-progress DAA path
before pending work is cancelled.  Install an i3c_bus_type shutdown
callback that engages this gate for master devices during system
shutdown, and use the same gate in i3c_master_unregister() so both
paths get identical guarantees.

Once the gate is engaged, the Hot-Join worker, i3c_master_do_daa_ext()
and i3c_set_hotjoin() all bail out cleanly, so Hot-Join IBIs that race
with shutdown become no-ops, direct DAA callers see -ENODEV, and sysfs
writers can no longer re-enable Hot-Join through ops->enable_hotjoin()
while the controller is going away.

No functional change for the steady-state runtime path; the new checks
only take effect once the controller has been marked as shutting down.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 drivers/i3c/master.c       | 52 +++++++++++++++++++++++++++-----------
 include/linux/i3c/master.h |  2 ++
 2 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index cdb5cb2aa65d..a59c4b744b36 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -368,14 +368,6 @@ static void i3c_device_remove(struct device *dev)
 		driver->remove(i3cdev);
 }
 
-const struct bus_type i3c_bus_type = {
-	.name = "i3c",
-	.match = i3c_device_match,
-	.probe = i3c_device_probe,
-	.remove = i3c_device_remove,
-};
-EXPORT_SYMBOL_GPL(i3c_bus_type);
-
 static enum i3c_addr_slot_status
 i3c_bus_get_addr_slot_status_mask(struct i3c_bus *bus, u16 addr, u32 mask)
 {
@@ -637,7 +629,8 @@ static void i3c_master_hj_work_fn(struct work_struct *work)
 {
 	struct i3c_master_controller *master = container_of(work, typeof(*master), hj_work);
 
-	i3c_master_do_daa(master);
+	if (!master->shutting_down)
+		i3c_master_do_daa(master);
 }
 
 static int i3c_set_hotjoin(struct i3c_master_controller *master, bool enable)
@@ -658,7 +651,9 @@ static int i3c_set_hotjoin(struct i3c_master_controller *master, bool enable)
 
 	i3c_bus_maintenance_lock(&master->bus);
 
-	if (enable)
+	if (master->shutting_down)
+		ret = -ENODEV;
+	else if (enable)
 		ret = master->ops->enable_hotjoin(master);
 	else
 		ret = master->ops->disable_hotjoin(master);
@@ -837,6 +832,30 @@ static const struct device_type i3c_masterdev_type = {
 	.groups	= i3c_masterdev_groups,
 };
 
+static void i3c_master_shutdown(struct i3c_master_controller *master)
+{
+	i3c_bus_maintenance_lock(&master->bus);
+	master->shutting_down = true;
+	i3c_bus_maintenance_unlock(&master->bus);
+
+	cancel_work_sync(&master->hj_work);
+}
+
+static void i3c_device_shutdown(struct device *dev)
+{
+	if (dev->type == &i3c_masterdev_type)
+		i3c_master_shutdown(dev_to_i3cmaster(dev));
+}
+
+const struct bus_type i3c_bus_type = {
+	.name = "i3c",
+	.match = i3c_device_match,
+	.probe = i3c_device_probe,
+	.remove = i3c_device_remove,
+	.shutdown = i3c_device_shutdown,
+};
+EXPORT_SYMBOL_GPL(i3c_bus_type);
+
 static int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
 			    unsigned long max_i2c_scl_rate)
 {
@@ -1846,10 +1865,13 @@ int i3c_master_do_daa_ext(struct i3c_master_controller *master, bool rstdaa)
 
 	i3c_bus_maintenance_lock(&master->bus);
 
-	if (rstdaa)
-		rstret = i3c_master_rstdaa_locked(master, I3C_BROADCAST_ADDR);
-
-	ret = master->ops->do_daa(master);
+	if (master->shutting_down) {
+		ret = -ENODEV;
+	} else {
+		if (rstdaa)
+			rstret = i3c_master_rstdaa_locked(master, I3C_BROADCAST_ADDR);
+		ret = master->ops->do_daa(master);
+	}
 
 	i3c_bus_maintenance_unlock(&master->bus);
 
@@ -3166,7 +3188,7 @@ EXPORT_SYMBOL_GPL(i3c_master_register);
 void i3c_master_unregister(struct i3c_master_controller *master)
 {
 	i3c_bus_notify(&master->bus, I3C_NOTIFY_BUS_REMOVE);
-	cancel_work_sync(&master->hj_work);
+	i3c_master_shutdown(master);
 
 	if (master->ops->set_dev_nack_retry)
 		device_remove_file(&master->dev, &dev_attr_dev_nack_retry_count);
diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
index eb5c51608bd7..77e63082b06e 100644
--- a/include/linux/i3c/master.h
+++ b/include/linux/i3c/master.h
@@ -511,6 +511,7 @@ struct i3c_master_controller_ops {
  * @hotjoin: true if the master support hotjoin
  * @rpm_allowed: true if Runtime PM allowed
  * @rpm_ibi_allowed: true if IBI and Hot-Join allowed while runtime suspended
+ * @shutting_down: set to true when master begins shutdown or unregister
  * @boardinfo.i3c: list of I3C  boardinfo objects
  * @boardinfo.i2c: list of I2C boardinfo objects
  * @boardinfo: board-level information attached to devices connected on the bus
@@ -539,6 +540,7 @@ struct i3c_master_controller {
 	unsigned int hotjoin: 1;
 	unsigned int rpm_allowed: 1;
 	unsigned int rpm_ibi_allowed: 1;
+	bool shutting_down;
 	struct {
 		struct list_head i3c;
 		struct list_head i2c;
-- 
2.51.0