[PATCH v3 2/3] firmware: arm_scmi: Pre-register protocol, name tupples for standard protocols

[Hans de Goede]

From: Cristian Marussi <cristian.marussi at arm.com>

Driver module auto-loading requires the devices to already be created for
udev to get the necessary uevents based on which udev auto-loads modules.
But SCMI devices are only created after their { protocol, name } tupples
have been registered 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.

Pre-register the tupples for standard protocols to break this circular
dependency.

Tested-by: Hans de Goede <johannes.goede at oss.qualcomm.com>
Signed-off-by: Cristian Marussi <cristian.marussi at arm.com>
Signed-off-by: Hans de Goede <johannes.goede at oss.qualcomm.com>
---
Changes in v3:
- Drop adding of a bus uevent function this is already done
- Update comments and commit message with a better explanation of why
- Link to v1/RFC: https://patch.msgid.link/20250203100154.140877-2-cristian.marussi@arm.com
---
 drivers/firmware/arm_scmi/bus.c | 47 ++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 7 deletions(-)

diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
index d12d5de15a1a..111727904a89 100644
--- a/drivers/firmware/arm_scmi/bus.c
+++ b/drivers/firmware/arm_scmi/bus.c
@@ -77,12 +77,13 @@ static int scmi_protocol_device_request(const struct scmi_device_id *id_table)
 	if (phead) {
 		head = phead;
 		list_for_each_entry(rdev, head, node) {
+			/* pr_debug() because dups are expected for std protocols */
 			if (!strcmp(rdev->id_table->name, id_table->name)) {
-				pr_err("Ignoring duplicate request [%d] %s\n",
-				       rdev->id_table->protocol_id,
-				       rdev->id_table->name);
-				ret = -EINVAL;
-				goto out;
+				pr_debug("Device already requested [%d] %s\n",
+					 rdev->id_table->protocol_id,
+					 rdev->id_table->name);
+				mutex_unlock(&scmi_requested_devices_mtx);
+				return 0;
 			}
 		}
 	}
@@ -579,17 +580,49 @@ static void scmi_devices_unregister(void)
 	bus_for_each_dev(&scmi_bus_type, NULL, NULL, __scmi_devices_unregister);
 }
 
+/* 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 int __init scmi_bus_init(void)
 {
 	int retval;
 
 	retval = bus_register(&scmi_bus_type);
-	if (retval)
+	if (retval) {
 		pr_err("SCMI protocol bus register failed (%d)\n", retval);
+		return retval;
+	}
+
+	/*
+	 * Driver module auto-loading requires the devices to already be created
+	 * for udev to get the necessary uevents. But the devices are only
+	 * created after their { protocol, name } tupples have been registered
+	 * which is done from scmi_driver_register(). Pre-register the tupples
+	 * for known (in tree) drivers to break this circular dependency.
+	 */
+	retval = scmi_protocol_table_register(scmi_std_id_table);
+	if (retval) {
+		bus_unregister(&scmi_bus_type);
+		return retval;
+	}
 
 	pr_info("SCMI protocol bus registered\n");
 
-	return retval;
+	return 0;
 }
 subsys_initcall(scmi_bus_init);
 
-- 
2.55.0