remoteproc: stm32: fix mbox_send_message call

mbox_send_message is called by passing a local dummy message or
a function parameter. As the message is queued, it is dereferenced.
This works because the message field is not used by the stm32 ipcc
driver, but it is not clean.

Fix by passing a constant string in all cases.

The associated comments are removed because rproc should not have to
deal with the behavior of the mailbox frame.
Reported-by: NBjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: NArnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20210420091922.29429-1-arnaud.pouliquen@foss.st.comSigned-off-by: NBjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/stm32_rproc.c

@@ -474,14 +474,12 @@ static int stm32_rproc_attach(struct rproc *rproc)
 static int stm32_rproc_detach(struct rproc *rproc)
 {
 	struct stm32_rproc *ddata = rproc->priv;
-	int err, dummy_data, idx;
+	int err, idx;
 
 	/* Inform the remote processor of the detach */
 	idx = stm32_rproc_mbox_idx(rproc, STM32_MBX_DETACH);
 	if (idx >= 0 && ddata->mb[idx].chan) {
-		/* A dummy data is sent to allow to block on transmit */
-		err = mbox_send_message(ddata->mb[idx].chan,
-					&dummy_data);
+		err = mbox_send_message(ddata->mb[idx].chan, "stop");
 		if (err < 0)
 			dev_warn(&rproc->dev, "warning: remote FW detach without ack\n");
 	}
@@ -493,15 +491,13 @@ static int stm32_rproc_detach(struct rproc *rproc)
 static int stm32_rproc_stop(struct rproc *rproc)
 {
 	struct stm32_rproc *ddata = rproc->priv;
-	int err, dummy_data, idx;
+	int err, idx;
 
 	/* request shutdown of the remote processor */
 	if (rproc->state != RPROC_OFFLINE) {
 		idx = stm32_rproc_mbox_idx(rproc, STM32_MBX_SHUTDOWN);
 		if (idx >= 0 && ddata->mb[idx].chan) {
-			/* a dummy data is sent to allow to block on transmit */
-			err = mbox_send_message(ddata->mb[idx].chan,
-						&dummy_data);
+			err = mbox_send_message(ddata->mb[idx].chan, "detach");
 			if (err < 0)
 				dev_warn(&rproc->dev, "warning: remote FW shutdown without ack\n");
 		}
@@ -556,7 +552,7 @@ static void stm32_rproc_kick(struct rproc *rproc, int vqid)
 			continue;
 		if (!ddata->mb[i].chan)
 			return;
-		err = mbox_send_message(ddata->mb[i].chan, (void *)(long)vqid);
+		err = mbox_send_message(ddata->mb[i].chan, "kick");
 		if (err < 0)
 			dev_err(&rproc->dev, "%s: failed (%s, err:%d)\n",
 				__func__, ddata->mb[i].name, err);