firmware: arm_scmi: Add compatibility checks for shmem node

The shared memory node used for communication between the firmware and
the OS should be compatible with "arm,scmi-shmem". Add the check for the
same while parsing the node before fetching the memory regions.

Link: https://lore.kernel.org/r/20210602073851.1005607-2-sudeep.holla@arm.com
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Cristian Marussi <cristian.marussi@arm.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Jim Quinlan <jim2101024@gmail.com>
Cc: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/mailbox.c

@@ -69,6 +69,9 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 		return -ENOMEM;
 
 	shmem = of_parse_phandle(cdev->of_node, "shmem", idx);
+	if (!of_device_is_compatible(shmem, "arm,scmi-shmem"))
+		return -ENXIO;
+
 	ret = of_address_to_resource(shmem, 0, &res);
 	of_node_put(shmem);
 	if (ret) {

drivers/firmware/arm_scmi/smc.c

@@ -76,6 +76,9 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 		return -ENOMEM;
 
 	np = of_parse_phandle(cdev->of_node, "shmem", 0);
+	if (!of_device_is_compatible(np, "arm,scmi-shmem"))
+		return -ENXIO;
+
 	ret = of_address_to_resource(np, 0, &res);
 	of_node_put(np);
 	if (ret) {