firmware: scmi: smt: add a polling completion method

Since u-boot does not support interrupt, implement a polling completion
method on smt status with a timeout.

Change-Id: I0e4ef68cb7da51975530bf1c5de7edd9bf5a6d32
Signed-off-by: Michel JAOUEN <michel.jaouen@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/u-boot/+/446888
Reviewed-by: Patrice CHOTARD <patrice.chotard@foss.st.com>
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>
ACI: CIBUILD <MDG-smet-aci-builds@list.st.com>
Domain-Review: Patrick DELAUNAY <patrick.delaunay@foss.st.com>

Author: jamike

drivers/firmware/scmi/smt.c

@@ -17,6 +17,7 @@
 #include <dm/ofnode.h>
 #include <linux/compat.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/ioport.h>
 
 #include "smt.h"
@@ -129,6 +130,26 @@ int scmi_read_resp_from_smt(struct udevice *dev, struct scmi_smt *smt,
 	return 0;
 }
 
+/**
+ * Wait SCMI message from a SMT shared buffer @smt and copy it into @msg.
+ * Return 0 on success and with a negative errno in case of error.
+ */
+int scmi_wait_resp_from_smt(struct udevice *dev, struct scmi_smt *smt,
+			    struct scmi_msg *msg,  ulong timeout_us)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+	__le32 status;
+	int ret;
+
+	ret = readl_poll_timeout(&hdr->channel_status, status, status &
+				 SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE,
+				 timeout_us);
+	if (ret)
+		return ret;
+
+	return scmi_read_resp_from_smt(dev, smt, msg);
+}
+
 /**
  * Clear SMT flags in shared buffer to allow further message exchange
  */

drivers/firmware/scmi/smt.h

@@ -106,6 +106,17 @@ int scmi_read_resp_from_smt(struct udevice *dev, struct scmi_smt *smt,
 
 void scmi_clear_smt_channel(struct scmi_smt *smt);
 
+/*
+ * Wait SCMI message from a SMT shared memory
+ * @dev: SCMI device
+ * @smt: Reference to shared memory using SMT header
+ * @msg: Output SCMI message received
+ * @timeout_us:	The maximum time to wait for a message to be available, in
+ *		micro-seconds. A value of 0 does not wait at all.
+ */
+int scmi_wait_resp_from_smt(struct udevice *dev, struct scmi_smt *smt,
+			    struct scmi_msg *msg, ulong timeout_us);
+
 /*
  * Write SCMI message to SMT_MSG shared memory
  * @dev: SCMI device