[PATCH 2/2] mailbox: add support for clients to request channels by arguments

[Tudor Ambarus]

There are clients that can discover channel identifiers at runtime by
parsing a shared memory for example, as in the ACPM interface's case.

Supply a new framework API: mbox_request_channel_by_args().

It works by supplying the usual client pointer as the first argument and
a pointer to a ``const struct mbox_xlate_args`` as a second. The newly
introduced struct is modeled after ``struct of_phandle_args``. The API
will search the client's node for a ``mbox`` phandle, identify the
controller's device node, and then call that controller's xlate() method
that will return a pointer to a mbox_chan or a ERR_PTR. The binding
between the channel and the client is done in the typical way.

Signed-off-by: Tudor Ambarus <tudor.ambarus at linaro.org>
---
 drivers/mailbox/mailbox.c          | 57 ++++++++++++++++++++++++++++++++++++++
 include/linux/mailbox.h            | 17 ++++++++++++
 include/linux/mailbox_client.h     |  3 ++
 include/linux/mailbox_controller.h |  4 +++
 4 files changed, 81 insertions(+)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index d3d26a2c9895..07ea32ebab80 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -467,6 +467,63 @@ struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
 }
 EXPORT_SYMBOL_GPL(mbox_request_channel_byname);
 
+/**
+ * mbox_request_channel_by_args - request a mailbox channel using client's
+ * channel identifiers.
+ * @cl: identity of the client requesting the channel.
+ * @spec: arguments that describe the channel.
+ *
+ * Used by clients that can discover the channel identifiers at runtime (by
+ * parsing a shared memory for example). The description of
+ * mbox_request_channel() applies here as well.
+ *
+ * Return: Pointer to the channel assigned to the client if successful.
+ *         ERR_PTR for request failure.
+ */
+struct mbox_chan *mbox_request_channel_by_args(struct mbox_client *cl,
+					const struct mbox_xlate_args *spec)
+{
+	struct device *dev = cl->dev;
+	struct mbox_controller *mbox;
+	struct device_node *mbox_np;
+	struct mbox_chan *chan;
+	int ret;
+
+	if (!dev || !dev->of_node) {
+		pr_debug("%s: No owner device node\n", __func__);
+		return ERR_PTR(-ENODEV);
+	}
+
+	mbox_np = of_parse_phandle(dev_of_node(dev), "mbox", 0);
+	if (!mbox_np)
+		return ERR_PTR(-ENODEV);
+
+	mutex_lock(&con_mutex);
+
+	chan = ERR_PTR(-EPROBE_DEFER);
+	list_for_each_entry(mbox, &mbox_cons, node)
+		if (mbox->dev->of_node == mbox_np && mbox->xlate) {
+			chan = mbox->xlate(mbox, spec);
+			if (!IS_ERR(chan))
+				break;
+		}
+
+	of_node_put(mbox_np);
+
+	if (IS_ERR(chan)) {
+		mutex_unlock(&con_mutex);
+		return chan;
+	}
+
+	ret = __mbox_bind_client(chan, cl);
+	if (ret)
+		chan = ERR_PTR(ret);
+
+	mutex_unlock(&con_mutex);
+	return chan;
+}
+EXPORT_SYMBOL_GPL(mbox_request_channel_by_args);
+
 /**
  * mbox_free_channel - The client relinquishes control of a mailbox
  *			channel by this call.
diff --git a/include/linux/mailbox.h b/include/linux/mailbox.h
new file mode 100644
index 000000000000..cef88c5ae49d
--- /dev/null
+++ b/include/linux/mailbox.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2024 Linaro Ltd.
+ */
+
+#ifndef __LINUX_MAILBOX_H
+#define __LINUX_MAILBOX_H
+
+#include <linux/types.h>
+
+#define MBOX_XLATE_MAX_ARGS 16
+struct mbox_xlate_args {
+	int args_count;
+	u32 args[MBOX_XLATE_MAX_ARGS];
+};
+
+#endif /* __LINUX_MAILBOX_H */
diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
index 734694912ef7..a9f4d108c48c 100644
--- a/include/linux/mailbox_client.h
+++ b/include/linux/mailbox_client.h
@@ -9,6 +9,7 @@
 
 #include <linux/of.h>
 #include <linux/device.h>
+#include <linux/mailbox.h>
 
 struct mbox_chan;
 
@@ -41,6 +42,8 @@ int mbox_bind_client(struct mbox_chan *chan, struct mbox_client *cl);
 struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
 					      const char *name);
 struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
+struct mbox_chan *mbox_request_channel_by_args(struct mbox_client *cl,
+			     const struct mbox_xlate_args *spec);
 int mbox_send_message(struct mbox_chan *chan, void *mssg);
 int mbox_flush(struct mbox_chan *chan, unsigned long timeout);
 void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index 6fee33cb52f5..dfddcf966f9f 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -8,6 +8,7 @@
 #include <linux/hrtimer.h>
 #include <linux/device.h>
 #include <linux/completion.h>
+#include <linux/mailbox.h>
 
 struct mbox_chan;
 
@@ -67,6 +68,7 @@ struct mbox_chan_ops {
  * @txpoll_period:	If 'txdone_poll' is in effect, the API polls for
  *			last TX's status after these many millisecs
  * @of_xlate:		Controller driver specific mapping of channel via DT
+ * @xlate:		Controller driver specific mapping of channel
  * @poll_hrt:		API private. hrtimer used to poll for TXDONE on all
  *			channels.
  * @node:		API private. To hook into list of controllers.
@@ -81,6 +83,8 @@ struct mbox_controller {
 	unsigned txpoll_period;
 	struct mbox_chan *(*of_xlate)(struct mbox_controller *mbox,
 				      const struct of_phandle_args *sp);
+	struct mbox_chan *(*xlate)(struct mbox_controller *mbox,
+				   const struct mbox_xlate_args *sp);
 	/* Internal to API */
 	struct hrtimer poll_hrt;
 	spinlock_t poll_hrt_lock;

-- 
2.47.1.613.gc27f4b7a9f-goog