firmware: arm_scmi: Add protocol versioning checks

Platform and agent supported protocols versions do not necessarily match.

When talking to an older SCMI platform, supporting only older protocol
versions, the kernel SCMI agent will downgrade the version of the used
protocol to match the platform and avoid compatibility issues.

In the case where the kernel/OSPM agent happens to communicate with a
newer platform which can support newer protocol versions unknown to
the agent, and potentially backward incompatible, the agent currently
carries on, silently, in a best-effort approach.

Note that the SCMI specification doesn't provide means to explicitly
detect the protocol versions used by the agents, neither it is required
to support multiple, older, protocol versions.

Add an explicit protocol version check to let the agent detect when this
version mismatch happens and warn the user about this condition.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20231201135858.2367651-1-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Author: cris-ma

drivers/firmware/arm_scmi/base.c

@@ -13,6 +13,9 @@
 #include "common.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x20000
+
 #define SCMI_BASE_NUM_SOURCES		1
 #define SCMI_BASE_MAX_CMD_ERR_COUNT	1024
 
@@ -385,7 +388,7 @@ static int scmi_base_protocol_init(const struct scmi_protocol_handle *ph)
 
 	rev->major_ver = PROTOCOL_REV_MAJOR(version),
 	rev->minor_ver = PROTOCOL_REV_MINOR(version);
-	ph->set_priv(ph, rev);
+	ph->set_priv(ph, rev, version);
 
 	ret = scmi_base_attributes_get(ph);
 	if (ret)
@@ -423,6 +426,7 @@ static const struct scmi_protocol scmi_base = {
 	.instance_init = &scmi_base_protocol_init,
 	.ops = NULL,
 	.events = &base_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(base, scmi_base)

drivers/firmware/arm_scmi/clock.c

@@ -12,6 +12,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x20001
+
 enum scmi_clock_protocol_cmd {
 	CLOCK_ATTRIBUTES = 0x3,
 	CLOCK_DESCRIBE_RATES = 0x4,
@@ -961,7 +964,7 @@ static int scmi_clock_protocol_init(const struct scmi_protocol_handle *ph)
 	}
 
 	cinfo->version = version;
-	return ph->set_priv(ph, cinfo);
+	return ph->set_priv(ph, cinfo, version);
 }
 
 static const struct scmi_protocol scmi_clock = {
@@ -970,6 +973,7 @@ static const struct scmi_protocol scmi_clock = {
 	.instance_init = &scmi_clock_protocol_init,
 	.ops = &clk_proto_ops,
 	.events = &clk_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(clock, scmi_clock)

drivers/firmware/arm_scmi/driver.c

@@ -85,6 +85,7 @@ struct scmi_xfers_info {
  * @gid: A reference for per-protocol devres management.
  * @users: A refcount to track effective users of this protocol.
  * @priv: Reference for optional protocol private data.
+ * @version: Protocol version supported by the platform as detected at runtime.
  * @ph: An embedded protocol handle that will be passed down to protocol
  *	initialization code to identify this instance.
  *
@@ -97,6 +98,7 @@ struct scmi_protocol_instance {
 	void				*gid;
 	refcount_t			users;
 	void				*priv;
+	unsigned int			version;
 	struct scmi_protocol_handle	ph;
 };
 
@@ -1392,15 +1394,17 @@ static int version_get(const struct scmi_protocol_handle *ph, u32 *version)
  *
  * @ph: A reference to the protocol handle.
  * @priv: The private data to set.
+ * @version: The detected protocol version for the core to register.
  *
  * Return: 0 on Success
  */
 static int scmi_set_protocol_priv(const struct scmi_protocol_handle *ph,
-				  void *priv)
+				  void *priv, u32 version)
 {
 	struct scmi_protocol_instance *pi = ph_to_pi(ph);
 
 	pi->priv = priv;
+	pi->version = version;
 
 	return 0;
 }
@@ -1849,6 +1853,12 @@ scmi_alloc_init_protocol_instance(struct scmi_info *info,
 	devres_close_group(handle->dev, pi->gid);
 	dev_dbg(handle->dev, "Initialized protocol: 0x%X\n", pi->proto->id);
 
+	if (pi->version > proto->supported_version)
+		dev_warn(handle->dev,
+			 "Detected UNSUPPORTED higher version 0x%X for protocol 0x%X."
+			 "Backward compatibility is NOT assured.\n",
+			 pi->version, pi->proto->id);
+
 	return pi;
 
 clean:

drivers/firmware/arm_scmi/perf.c

@@ -24,6 +24,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x40000
+
 #define MAX_OPPS		32
 
 enum scmi_performance_protocol_cmd {
@@ -1104,7 +1107,7 @@ static int scmi_perf_protocol_init(const struct scmi_protocol_handle *ph)
 	if (ret)
 		return ret;
 
-	return ph->set_priv(ph, pinfo);
+	return ph->set_priv(ph, pinfo, version);
 }
 
 static const struct scmi_protocol scmi_perf = {
@@ -1113,6 +1116,7 @@ static const struct scmi_protocol scmi_perf = {
 	.instance_init = &scmi_perf_protocol_init,
 	.ops = &perf_proto_ops,
 	.events = &perf_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(perf, scmi_perf)

drivers/firmware/arm_scmi/power.c

@@ -13,6 +13,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x30000
+
 enum scmi_power_protocol_cmd {
 	POWER_DOMAIN_ATTRIBUTES = 0x3,
 	POWER_STATE_SET = 0x4,
@@ -328,7 +331,7 @@ static int scmi_power_protocol_init(const struct scmi_protocol_handle *ph)
 
 	pinfo->version = version;
 
-	return ph->set_priv(ph, pinfo);
+	return ph->set_priv(ph, pinfo, version);
 }
 
 static const struct scmi_protocol scmi_power = {
@@ -337,6 +340,7 @@ static const struct scmi_protocol scmi_power = {
 	.instance_init = &scmi_power_protocol_init,
 	.ops = &power_proto_ops,
 	.events = &power_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(power, scmi_power)

drivers/firmware/arm_scmi/powercap.c

@@ -17,6 +17,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x20000
+
 enum scmi_powercap_protocol_cmd {
 	POWERCAP_DOMAIN_ATTRIBUTES = 0x3,
 	POWERCAP_CAP_GET = 0x4,
@@ -975,7 +978,7 @@ scmi_powercap_protocol_init(const struct scmi_protocol_handle *ph)
 	}
 
 	pinfo->version = version;
-	return ph->set_priv(ph, pinfo);
+	return ph->set_priv(ph, pinfo, version);
 }
 
 static const struct scmi_protocol scmi_powercap = {
@@ -984,6 +987,7 @@ static const struct scmi_protocol scmi_powercap = {
 	.instance_init = &scmi_powercap_protocol_init,
 	.ops = &powercap_proto_ops,
 	.events = &powercap_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(powercap, scmi_powercap)

drivers/firmware/arm_scmi/protocols.h

@@ -174,7 +174,8 @@ struct scmi_protocol_handle {
 	struct device *dev;
 	const struct scmi_xfer_ops *xops;
 	const struct scmi_proto_helpers_ops *hops;
-	int (*set_priv)(const struct scmi_protocol_handle *ph, void *priv);
+	int (*set_priv)(const struct scmi_protocol_handle *ph, void *priv,
+			u32 version);
 	void *(*get_priv)(const struct scmi_protocol_handle *ph);
 };
 
@@ -311,6 +312,10 @@ typedef int (*scmi_prot_init_ph_fn_t)(const struct scmi_protocol_handle *);
  * @ops: Optional reference to the operations provided by the protocol and
  *	 exposed in scmi_protocol.h.
  * @events: An optional reference to the events supported by this protocol.
+ * @supported_version: The highest version currently supported for this
+ *		       protocol by the agent. Each protocol implementation
+ *		       in the agent is supposed to downgrade to match the
+ *		       protocol version supported by the platform.
  */
 struct scmi_protocol {
 	const u8				id;
@@ -319,6 +324,7 @@ struct scmi_protocol {
 	const scmi_prot_init_ph_fn_t		instance_deinit;
 	const void				*ops;
 	const struct scmi_protocol_events	*events;
+	unsigned int				supported_version;
 };
 
 #define DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(name, proto)	\

drivers/firmware/arm_scmi/reset.c

@@ -13,6 +13,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x30000
+
 enum scmi_reset_protocol_cmd {
 	RESET_DOMAIN_ATTRIBUTES = 0x3,
 	RESET = 0x4,
@@ -343,7 +346,7 @@ static int scmi_reset_protocol_init(const struct scmi_protocol_handle *ph)
 	}
 
 	pinfo->version = version;
-	return ph->set_priv(ph, pinfo);
+	return ph->set_priv(ph, pinfo, version);
 }
 
 static const struct scmi_protocol scmi_reset = {
@@ -352,6 +355,7 @@ static const struct scmi_protocol scmi_reset = {
 	.instance_init = &scmi_reset_protocol_init,
 	.ops = &reset_proto_ops,
 	.events = &reset_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(reset, scmi_reset)

drivers/firmware/arm_scmi/sensors.c

@@ -14,6 +14,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x30000
+
 #define SCMI_MAX_NUM_SENSOR_AXIS	63
 #define	SCMIv2_SENSOR_PROTOCOL		0x10000
 
@@ -1138,7 +1141,7 @@ static int scmi_sensors_protocol_init(const struct scmi_protocol_handle *ph)
 	if (ret)
 		return ret;
 
-	return ph->set_priv(ph, sinfo);
+	return ph->set_priv(ph, sinfo, version);
 }
 
 static const struct scmi_protocol scmi_sensors = {
@@ -1147,6 +1150,7 @@ static const struct scmi_protocol scmi_sensors = {
 	.instance_init = &scmi_sensors_protocol_init,
 	.ops = &sensor_proto_ops,
 	.events = &sensor_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(sensors, scmi_sensors)

drivers/firmware/arm_scmi/system.c

@@ -13,6 +13,9 @@
 #include "protocols.h"
 #include "notify.h"
 
+/* Updated only after ALL the mandatory features for that version are merged */
+#define SCMI_PROTOCOL_SUPPORTED_VERSION		0x20000
+
 #define SCMI_SYSTEM_NUM_SOURCES		1
 
 enum scmi_system_protocol_cmd {
@@ -144,7 +147,7 @@ static int scmi_system_protocol_init(const struct scmi_protocol_handle *ph)
 	if (PROTOCOL_REV_MAJOR(pinfo->version) >= 0x2)
 		pinfo->graceful_timeout_supported = true;
 
-	return ph->set_priv(ph, pinfo);
+	return ph->set_priv(ph, pinfo, version);
 }
 
 static const struct scmi_protocol scmi_system = {
@@ -153,6 +156,7 @@ static const struct scmi_protocol scmi_system = {
 	.instance_init = &scmi_system_protocol_init,
 	.ops = NULL,
 	.events = &system_protocol_events,
+	.supported_version = SCMI_PROTOCOL_SUPPORTED_VERSION,
 };
 
 DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(system, scmi_system)