remoteproc: Introduce prepare and unprepare for subdevices

On rare occasions a subdevice might need to prepare some hardware
resources before a remote processor is booted, and clean up some
state after it has been shut down.

One such example is the IP Accelerator found in various Qualcomm
platforms, which is accessed directly from both the modem remoteproc
and the application subsystem and requires an intricate lockstep
process when bringing the modem up and down.
Tested-by: NFabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: NBjorn Andersson <bjorn.andersson@linaro.org>
[elder@linaro.org: minor description and comment edits]
Signed-off-by Alex Elder <elder@linaro.org>
Signed-off-by: NBjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/remoteproc_core.c

@@ -776,6 +776,30 @@ static int rproc_handle_resources(struct rproc *rproc,
 	return ret;
 }
 
+static int rproc_prepare_subdevices(struct rproc *rproc)
+{
+	struct rproc_subdev *subdev;
+	int ret;
+
+	list_for_each_entry(subdev, &rproc->subdevs, node) {
+		if (subdev->prepare) {
+			ret = subdev->prepare(subdev);
+			if (ret)
+				goto unroll_preparation;
+		}
+	}
+
+	return 0;
+
+unroll_preparation:
+	list_for_each_entry_continue_reverse(subdev, &rproc->subdevs, node) {
+		if (subdev->unprepare)
+			subdev->unprepare(subdev);
+	}
+
+	return ret;
+}
+
 static int rproc_start_subdevices(struct rproc *rproc)
 {
 	struct rproc_subdev *subdev;
@@ -810,6 +834,16 @@ static void rproc_stop_subdevices(struct rproc *rproc, bool crashed)
 	}
 }
 
+static void rproc_unprepare_subdevices(struct rproc *rproc)
+{
+	struct rproc_subdev *subdev;
+
+	list_for_each_entry_reverse(subdev, &rproc->subdevs, node) {
+		if (subdev->unprepare)
+			subdev->unprepare(subdev);
+	}
+}
+
 /**
  * rproc_coredump_cleanup() - clean up dump_segments list
  * @rproc: the remote processor handle
@@ -902,11 +936,18 @@ static int rproc_start(struct rproc *rproc, const struct firmware *fw)
 		rproc->table_ptr = loaded_table;
 	}
 
+	ret = rproc_prepare_subdevices(rproc);
+	if (ret) {
+		dev_err(dev, "failed to prepare subdevices for %s: %d\n",
+			rproc->name, ret);
+		return ret;
+	}
+
 	/* power up the remote processor */
 	ret = rproc->ops->start(rproc);
 	if (ret) {
 		dev_err(dev, "can't start rproc %s: %d\n", rproc->name, ret);
-		return ret;
+		goto unprepare_subdevices;
 	}
 
 	/* Start any subdevices for the remote processor */
@@ -914,8 +955,7 @@ static int rproc_start(struct rproc *rproc, const struct firmware *fw)
 	if (ret) {
 		dev_err(dev, "failed to probe subdevices for %s: %d\n",
 			rproc->name, ret);
-		rproc->ops->stop(rproc);
-		return ret;
+		goto stop_rproc;
 	}
 
 	rproc->state = RPROC_RUNNING;
@@ -923,6 +963,14 @@ static int rproc_start(struct rproc *rproc, const struct firmware *fw)
 	dev_info(dev, "remote processor %s is now up\n", rproc->name);
 
 	return 0;
+
+stop_rproc:
+	rproc->ops->stop(rproc);
+
+unprepare_subdevices:
+	rproc_unprepare_subdevices(rproc);
+
+	return ret;
 }
 
 /*
@@ -1035,6 +1083,8 @@ static int rproc_stop(struct rproc *rproc, bool crashed)
 		return ret;
 	}
 
+	rproc_unprepare_subdevices(rproc);
+
 	rproc->state = RPROC_OFFLINE;
 
 	dev_info(dev, "stopped remote processor %s\n", rproc->name);

include/linux/remoteproc.h

@@ -477,15 +477,19 @@ struct rproc {
 /**
  * struct rproc_subdev - subdevice tied to a remoteproc
  * @node: list node related to the rproc subdevs list
+ * @prepare: prepare function, called before the rproc is started
  * @start: start function, called after the rproc has been started
  * @stop: stop function, called before the rproc is stopped; the @crashed
  *	    parameter indicates if this originates from a recovery
+ * @unprepare: unprepare function, called after the rproc has been stopped
  */
 struct rproc_subdev {
 	struct list_head node;
 
+	int (*prepare)(struct rproc_subdev *subdev);
 	int (*start)(struct rproc_subdev *subdev);
 	void (*stop)(struct rproc_subdev *subdev, bool crashed);
+	void (*unprepare)(struct rproc_subdev *subdev);
 };
 
 /* we currently support only two vrings per rvdev */