[PATCH] firmware: arm_scmi: Ensure drivers provide a probe function

From: Sudeep Holla <redacted>

[ Upstream commit 5e469dac326555d2038d199a6329458cc82a34e5 ]

The bus probe callback calls the driver callback without further
checking. Better be safe than sorry and refuse registration of a driver
without a probe function to prevent a NULL pointer exception.

Cc: <redacted> # v4.19+
Link: https://lore.kernel.org/r/20210624095059.4010157-2-sudeep.holla@arm.com (local)
Fixes: 933c504424a2 ("firmware: arm_scmi: add scmi protocol bus to enumerate protocol devices")
Reported-by: Uwe Kleine-König <redacted>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Acked-by: Uwe Kleine-König <redacted>
Signed-off-by: Sudeep Holla <redacted>
---
Upstream commit 5e469dac326555d2038d199a6329458cc82a34e5 has been already
applied to stable/linux-5.13.y, this is a backport with conflicts resolved
for v4.19, v5.4 and v5.10. (SCMI stack did not even exist before 4.19)
---
 drivers/firmware/arm_scmi/bus.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
index 7a30952b463d..66d445b14e51 100644
--- a/drivers/firmware/arm_scmi/bus.c
+++ b/drivers/firmware/arm_scmi/bus.c

@@ -100,6 +100,9 @@ int scmi_driver_register(struct scmi_driver *driver, struct module *owner,
 {
 	int retval;
 
+	if (!driver->probe)
+		return -EINVAL;
+
 	driver->driver.bus = &scmi_bus_type;
 	driver->driver.name = driver->name;
 	driver->driver.owner = owner;

-- 
2.17.1