firmware: arm_scmi: Add mechanism to unpack message headers

In order to identify the message type when a response arrives, we need
a mechanism to unpack the message header similar to packing. Let's
add one.
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/driver.c

@@ -30,8 +30,14 @@
 #include "common.h"
 
 #define MSG_ID_MASK		GENMASK(7, 0)
+#define MSG_XTRACT_ID(hdr)	FIELD_GET(MSG_ID_MASK, (hdr))
 #define MSG_TYPE_MASK		GENMASK(9, 8)
+#define MSG_XTRACT_TYPE(hdr)	FIELD_GET(MSG_TYPE_MASK, (hdr))
+#define MSG_TYPE_COMMAND	0
+#define MSG_TYPE_DELAYED_RESP	2
+#define MSG_TYPE_NOTIFICATION	3
 #define MSG_PROTOCOL_ID_MASK	GENMASK(17, 10)
+#define MSG_XTRACT_PROT_ID(hdr)	FIELD_GET(MSG_PROTOCOL_ID_MASK, (hdr))
 #define MSG_TOKEN_ID_MASK	GENMASK(27, 18)
 #define MSG_XTRACT_TOKEN(hdr)	FIELD_GET(MSG_TOKEN_ID_MASK, (hdr))
 #define MSG_TOKEN_MAX		(MSG_XTRACT_TOKEN(MSG_TOKEN_ID_MASK) + 1)
@@ -214,6 +220,18 @@ static inline u32 pack_scmi_header(struct scmi_msg_hdr *hdr)
 		FIELD_PREP(MSG_PROTOCOL_ID_MASK, hdr->protocol_id);
 }
 
+/**
+ * unpack_scmi_header() - unpacks and records message and protocol id
+ *
+ * @msg_hdr: 32-bit packed message header sent from the platform
+ * @hdr: pointer to header to fetch message and protocol id.
+ */
+static inline void unpack_scmi_header(u32 msg_hdr, struct scmi_msg_hdr *hdr)
+{
+	hdr->id = MSG_XTRACT_ID(msg_hdr);
+	hdr->protocol_id = MSG_XTRACT_PROT_ID(msg_hdr);
+}
+
 /**
  * scmi_tx_prepare() - mailbox client callback to prepare for the transfer
  *