[PATCH v5 3/3] firmware: arm_scmi: Always create devices for standard protocols

[Hans de Goede]

Protocol driver module auto-loading requires the devices to already be
created for udev to get the necessary uevents based on which udev loads
modules. But SCMI devices are only created after their { protocol, name }
device-id has been added to the requested-devices list which is done from
scmi_driver_register().

This creates a circular dependency where device creation is waiting for
the driver to register and loading the module with the driver is waiting
for the device to be created.

Add a list of standard protocol device-ids and always create devices for
these without relying on these being added to the requested-devices list.

This removes the circular dependency, fixing module auto-loading.

Signed-off-by: Hans de Goede <johannes.goede at oss.qualcomm.com>
---
Changes in v5:
- This is a new patch in v5 replacing "Pre-register protocol, name tupples
  for standard protocol". Pre-registering requires
  scmi_protocol_device_request() to allow duplicate device-ids, but then if
  the first driver of two with duplicate devce-ids gets unloaded device
  creation for the second driver will fail. Allowing duplicates causes all
  kinds of problems, so this new approach avoids this.
---
 drivers/firmware/arm_scmi/bus.c | 48 +++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
index 6f667e4ffeed..10d15da76f19 100644
--- a/drivers/firmware/arm_scmi/bus.c
+++ b/drivers/firmware/arm_scmi/bus.c
@@ -505,6 +505,34 @@ _scmi_device_create(struct device_node *np, struct device *parent,
 	return sdev;
 }
 
+/* Standard protocols table */
+static const struct scmi_device_id scmi_std_id_table[] = {
+	{ SCMI_PROTOCOL_POWER, "genpd" },
+	{ SCMI_PROTOCOL_SYSTEM, "syspower" },
+	{ SCMI_PROTOCOL_PERF, "perf" },
+	{ SCMI_PROTOCOL_PERF, "cpufreq" },
+	{ SCMI_PROTOCOL_CLOCK, "clocks" },
+	{ SCMI_PROTOCOL_SENSOR, "hwmon" },
+	{ SCMI_PROTOCOL_SENSOR, "iiodev" },
+	{ SCMI_PROTOCOL_RESET, "reset" },
+	{ SCMI_PROTOCOL_VOLTAGE, "regulator" },
+	{ SCMI_PROTOCOL_POWERCAP, "powercap" },
+	{ SCMI_PROTOCOL_PINCTRL, "pinctrl" },
+	{ SCMI_PROTOCOL_PINCTRL, "pinctrl-imx" },
+	{ },
+};
+
+static bool scmi_device_id_in_std_id_table(const struct scmi_device_id *id)
+{
+	for (int i = 0; scmi_std_id_table[i].name[0]; i++) {
+		if (scmi_std_id_table[i].protocol_id == id->protocol_id &&
+		    !strcmp(scmi_std_id_table[i].name, id->name))
+			return true;
+	}
+
+	return false;
+}
+
 /**
  * scmi_device_create  - A method to create one or more SCMI devices
  *
@@ -534,11 +562,25 @@ struct scmi_device *scmi_device_create(struct device_node *np,
 {
 	struct list_head *phead;
 	struct scmi_requested_dev *rdev;
-	struct scmi_device *scmi_dev = NULL;
+	struct scmi_device *sdev, *scmi_dev = NULL;
 
 	if (name)
 		return _scmi_device_create(np, parent, protocol, name);
 
+	/*
+	 * Always create devices for standard protocols, even if the device-ids
+	 * have not been registered into scmi_requested_devices yet. This allows
+	 * auto-loading of SCMI protocol driver modules for standard protocols.
+	 */
+	for (int i = 0; scmi_std_id_table[i].name[0]; i++) {
+		if (scmi_std_id_table[i].protocol_id != protocol)
+			continue;
+
+		sdev = _scmi_device_create(np, parent, protocol, scmi_std_id_table[i].name);
+		if (sdev)
+			scmi_dev = sdev;
+	}
+
 	mutex_lock(&scmi_requested_devices_mtx);
 	phead = idr_find(&scmi_requested_devices, protocol);
 	/* Nothing to do. */
@@ -549,7 +591,9 @@ struct scmi_device *scmi_device_create(struct device_node *np,
 
 	/* Walk the list of requested devices for protocol and create them */
 	list_for_each_entry(rdev, phead, node) {
-		struct scmi_device *sdev;
+		/* Standard proto matches already have their dev created above */
+		if (scmi_device_id_in_std_id_table(rdev->id_table))
+			continue;
 
 		sdev = _scmi_device_create(np, parent,
 					   rdev->id_table->protocol_id,
-- 
2.55.0