remoteproc: Refactor function rproc_boot()

Refactor function rproc_boot() to properly deal with scenarios
where the remoteproc core needs to attach with a remote
processor that has already been booted by an external entity.
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Link: https://lore.kernel.org/r/20200714195035.1426873-7-mathieu.poirier@linaro.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/remoteproc_core.c

@@ -1497,7 +1497,7 @@ static int rproc_fw_boot(struct rproc *rproc, const struct firmware *fw)
  * Attach to remote processor - similar to rproc_fw_boot() but without
  * the steps that deal with the firmware image.
  */
-static int __maybe_unused rproc_actuate(struct rproc *rproc)
+static int rproc_actuate(struct rproc *rproc)
 {
 	struct device *dev = &rproc->dev;
 	int ret;
@@ -1908,12 +1908,17 @@ int rproc_boot(struct rproc *rproc)
 		goto unlock_mutex;
 	}
 
-	/* skip the boot process if rproc is already powered up */
+	/* skip the boot or attach process if rproc is already powered up */
 	if (atomic_inc_return(&rproc->power) > 1) {
 		ret = 0;
 		goto unlock_mutex;
 	}
 
+	if (rproc->state == RPROC_DETACHED) {
+		dev_info(dev, "attaching to %s\n", rproc->name);
+
+		ret = rproc_actuate(rproc);
+	} else {
 		dev_info(dev, "powering up %s\n", rproc->name);
 
 		/* load firmware */
@@ -1926,6 +1931,7 @@ int rproc_boot(struct rproc *rproc)
 		ret = rproc_fw_boot(rproc, firmware_p);
 
 		release_firmware(firmware_p);
+	}
 
 downref_rproc:
 	if (ret)