[PATCH v3] mailbox: add list of used channels to debugfs

[Wolfram Sang]

During development, it is useful to see which mailboxes are currently
obtained. Use a seq-file in debugfs to list the currently registered
controllers and their used channels. Example output from a Renesas R-Car
X5H based system:

189e0000.system-controller:
   0: c1000000.mailbox_test_send_to_recv
   1: c1000100.mailbox_test_recv_to_send
 128: c1000100.mailbox_test_recv_to_send
 129: c1000000.mailbox_test_send_to_recv
189e1000.system-controller:
   4: scmi_dev.1
   5: scmi_dev.2

Note that mailbox controllers currently can be instantiated at any
initcall stage. So, per-controller debugfs handling was discarded
because it is not clear when to create the root "mailbox"-debugfs entry.
A central file was chosen, similar to the GPIO subsystem, which is
independent of the initcall stage because it will be accessed only when
userspace is available anyhow.

Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---

Changes since v2:
* rebased on top of linux-next
  (used the wrong branch previously, I am sorry about that!)

 drivers/mailbox/mailbox.c | 57 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index 138ffbcd4fde..d3a29e361f33 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/cleanup.h>
+#include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/err.h>
@@ -16,6 +17,7 @@
 #include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/property.h>
+#include <linux/seq_file.h>
 #include <linux/spinlock.h>
 
 static LIST_HEAD(mbox_cons);
@@ -633,3 +635,58 @@ int devm_mbox_controller_register(struct device *dev,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(devm_mbox_controller_register);
+
+#ifdef CONFIG_DEBUG_FS
+static void *mbox_seq_start(struct seq_file *s, loff_t *pos)
+{
+	mutex_lock(&con_mutex);
+	return seq_list_start(&mbox_cons, *pos);
+}
+
+static void *mbox_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	return seq_list_next(v, &mbox_cons, pos);
+}
+
+static void mbox_seq_stop(struct seq_file *s, void *v)
+{
+	mutex_unlock(&con_mutex);
+}
+
+static int mbox_seq_show(struct seq_file *seq, void *v)
+{
+	const struct mbox_controller *mbox = list_entry(v, struct mbox_controller, node);
+
+	seq_printf(seq, "%s:\n", dev_name(mbox->dev));
+
+	for (unsigned int i = 0; i < mbox->num_chans; i++) {
+		struct mbox_chan *chan = &mbox->chans[i];
+
+		scoped_guard(spinlock_irqsave, &chan->lock) {
+			if (chan->cl) {
+				struct device *cl_dev = chan->cl->dev;
+
+				seq_printf(seq, " %3u: %s\n", i,
+					   cl_dev ? dev_name(cl_dev) : "NULL device");
+			}
+		}
+	}
+
+	return 0;
+}
+
+static const struct seq_operations mbox_sops = {
+	.start = mbox_seq_start,
+	.next = mbox_seq_next,
+	.stop = mbox_seq_stop,
+	.show = mbox_seq_show,
+};
+DEFINE_SEQ_ATTRIBUTE(mbox);
+
+static int __init mbox_init(void)
+{
+	debugfs_create_file("mailbox_summary", 0444, NULL, NULL, &mbox_fops);
+	return 0;
+}
+subsys_initcall(mbox_init);
+#endif	/* DEBUG_FS */
-- 
2.51.0