1 files changed, 94 insertions, 5 deletions

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 3ea64b22cf0d..34d77802c990 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -86,6 +86,12 @@ struct scmi_xfers_info {
  * @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.
+ * @negotiated_version: When the platform supports a newer protocol version,
+ *			the agent will try to negotiate with the platform the
+ *			usage of the newest version known to it, since
+ *			backward compatibility is NOT automatically assured.
+ *			This field is NON-zero when a successful negotiation
+ *			has completed.
  * @ph: An embedded protocol handle that will be passed down to protocol
  *	initialization code to identify this instance.
  *
@@ -99,6 +105,7 @@ struct scmi_protocol_instance {
 	refcount_t			users;
 	void				*priv;
 	unsigned int			version;
+	unsigned int			negotiated_version;
 	struct scmi_protocol_handle	ph;
 };
 
@@ -1754,10 +1761,44 @@ static void scmi_common_fastchannel_db_ring(struct scmi_fc_db_info *db)
 #endif
 }
 
+/**
+ * scmi_protocol_msg_check  - Check protocol message attributes
+ *
+ * @ph: A reference to the protocol handle.
+ * @message_id: The ID of the message to check.
+ * @attributes: A parameter to optionally return the retrieved message
+ *		attributes, in case of Success.
+ *
+ * An helper to check protocol message attributes for a specific protocol
+ * and message pair.
+ *
+ * Return: 0 on SUCCESS
+ */
+static int scmi_protocol_msg_check(const struct scmi_protocol_handle *ph,
+				   u32 message_id, u32 *attributes)
+{
+	int ret;
+	struct scmi_xfer *t;
+
+	ret = xfer_get_init(ph, PROTOCOL_MESSAGE_ATTRIBUTES,
+			    sizeof(__le32), 0, &t);
+	if (ret)
+		return ret;
+
+	put_unaligned_le32(message_id, t->tx.buf);
+	ret = do_xfer(ph, t);
+	if (!ret && attributes)
+		*attributes = get_unaligned_le32(t->rx.buf);
+	xfer_put(ph, t);
+
+	return ret;
+}
+
 static const struct scmi_proto_helpers_ops helpers_ops = {
 	.extended_name_get = scmi_common_extended_name_get,
 	.iter_response_init = scmi_iterator_init,
 	.iter_response_run = scmi_iterator_run,
+	.protocol_msg_check = scmi_protocol_msg_check,
 	.fastchannel_init = scmi_common_fastchannel_init,
 	.fastchannel_db_ring = scmi_common_fastchannel_db_ring,
 };
@@ -1782,6 +1823,44 @@ scmi_revision_area_get(const struct scmi_protocol_handle *ph)
 }
 
 /**
+ * scmi_protocol_version_negotiate  - Negotiate protocol version
+ *
+ * @ph: A reference to the protocol handle.
+ *
+ * An helper to negotiate a protocol version different from the latest
+ * advertised as supported from the platform: on Success backward
+ * compatibility is assured by the platform.
+ *
+ * Return: 0 on Success
+ */
+static int scmi_protocol_version_negotiate(struct scmi_protocol_handle *ph)
+{
+	int ret;
+	struct scmi_xfer *t;
+	struct scmi_protocol_instance *pi = ph_to_pi(ph);
+
+	/* At first check if NEGOTIATE_PROTOCOL_VERSION is supported ... */
+	ret = scmi_protocol_msg_check(ph, NEGOTIATE_PROTOCOL_VERSION, NULL);
+	if (ret)
+		return ret;
+
+	/* ... then attempt protocol version negotiation */
+	ret = xfer_get_init(ph, NEGOTIATE_PROTOCOL_VERSION,
+			    sizeof(__le32), 0, &t);
+	if (ret)
+		return ret;
+
+	put_unaligned_le32(pi->proto->supported_version, t->tx.buf);
+	ret = do_xfer(ph, t);
+	if (!ret)
+		pi->negotiated_version = pi->proto->supported_version;
+
+	xfer_put(ph, t);
+
+	return ret;
+}
+
+/**
  * scmi_alloc_init_protocol_instance  - Allocate and initialize a protocol
  * instance descriptor.
  * @info: The reference to the related SCMI instance.
@@ -1853,11 +1932,21 @@ 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);
+	if (pi->version > proto->supported_version) {
+		ret = scmi_protocol_version_negotiate(&pi->ph);
+		if (!ret) {
+			dev_info(handle->dev,
+				 "Protocol 0x%X successfully negotiated version 0x%X\n",
+				 proto->id, pi->negotiated_version);
+		} else {
+			dev_warn(handle->dev,
+				 "Detected UNSUPPORTED higher version 0x%X for protocol 0x%X.\n",
+				 pi->version, pi->proto->id);
+			dev_warn(handle->dev,
+				 "Trying version 0x%X. Backward compatibility is NOT assured.\n",
+				 pi->proto->supported_version);
+		}
+	}
 
 	return pi;