For some PTP devices, they have the capability to loop back the periodic
output signal for debugging, such as the ptp_qoriq device. So add the
generic interfaces to set the periodic output signal loopback, rather
than each vendor having a different implementation.

Show how many channels support the periodic output signal loopback:
$ cat /sys/kernel/debug/ptp<N>/n_perout_loopback

Enable the loopback of the periodic output signal of channel X:
$ echo <X> 1 > /sys/kernel/debug/ptp<N>/perout_loopback

Disable the loopback of the periodic output signal of channel X:
$ echo <X> 0 > /sys/kernel/debug/ptp<N>/perout_loopback

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
 drivers/ptp/ptp_clock.c          | 66 ++++++++++++++++++++++++++++++++
 include/linux/ptp_clock_kernel.h | 10 +++++
 2 files changed, 76 insertions(+)

diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index 5739a57958c7..e4a5658e82b3 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -248,6 +248,66 @@ static void ptp_aux_kworker(struct kthread_work *work)
 		kthread_queue_delayed_work(ptp->kworker, &ptp->aux_work, delay);
 }
 
+static ssize_t ptp_n_perout_loopback_read(struct file *filep,
+					  char __user *buffer,
+					  size_t count, loff_t *pos)
+{
+	struct ptp_clock *ptp = filep->private_data;
+	char buf[12] = {};
+
+	snprintf(buf, sizeof(buf), "%d\n", ptp->info->n_per_lp);
+
+	return simple_read_from_buffer(buffer, count, pos, buf, strlen(buf));
+}
+
+static const struct file_operations ptp_n_perout_loopback_fops = {
+	.owner	= THIS_MODULE,
+	.open	= simple_open,
+	.read	= ptp_n_perout_loopback_read,
+};
+
+static ssize_t ptp_perout_loopback_write(struct file *filep,
+					 const char __user *buffer,
+					 size_t count, loff_t *ppos)
+{
+	struct ptp_clock *ptp = filep->private_data;
+	struct ptp_clock_info *ops = ptp->info;
+	int len, cnt, enable, err;
+	unsigned int index;
+	char buf[32] = {};
+
+	if (*ppos || !count)
+		return -EINVAL;
+
+	if (count >= sizeof(buf))
+		return -ENOSPC;
+
+	len = simple_write_to_buffer(buf, sizeof(buf) - 1,
+				     ppos, buffer, count);
+	if (len < 0)
+		return len;
+
+	buf[len] = '\0';
+	cnt = sscanf(buf, "%u %d", &index, &enable);
+	if (cnt != 2)
+		return -EINVAL;
+
+	if (index >= ops->n_per_lp)
+		return -EINVAL;
+
+	err = ops->perout_loopback(ops, index, enable ? 1 : 0);
+	if (err)
+		return err;
+
+	return count;
+}
+
+static const struct file_operations ptp_perout_loopback_ops = {
+	.owner   = THIS_MODULE,
+	.open    = simple_open,
+	.write	 = ptp_perout_loopback_write,
+};
+
 /* public interface */
 
 struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
@@ -389,6 +449,12 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 	/* Debugfs initialization */
 	snprintf(debugfsname, sizeof(debugfsname), "ptp%d", ptp->index);
 	ptp->debugfs_root = debugfs_create_dir(debugfsname, NULL);
+	if (info->n_per_lp > 0 && info->perout_loopback) {
+		debugfs_create_file("n_perout_loopback", 0400, ptp->debugfs_root,
+				    ptp, &ptp_n_perout_loopback_fops);
+		debugfs_create_file("perout_loopback", 0200, ptp->debugfs_root,
+				    ptp, &ptp_perout_loopback_ops);
+	}
 
 	return ptp;
 
diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
index 7dd7951b23d5..884364596dd3 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -67,6 +67,8 @@ struct ptp_system_timestamp {
  * @n_ext_ts:  The number of external time stamp channels.
  * @n_per_out: The number of programmable periodic signals.
  * @n_pins:    The number of programmable pins.
+ * @n_per_lp:  The number of channels that support loopback the periodic
+ *             output signal.
  * @pps:       Indicates whether the clock supports a PPS callback.
  *
  * @supported_perout_flags:  The set of flags the driver supports for the
@@ -175,6 +177,11 @@ struct ptp_system_timestamp {
  *                scheduling time (>=0) or negative value in case further
  *                scheduling is not required.
  *
+ * @perout_loopback: Request driver to enable or disable the periodic output
+ *                   signal loopback.
+ *                   parameter index: index of the periodic output signal channel.
+ *                   parameter on: caller passes one to enable or zero to disable.
+ *
  * Drivers should embed their ptp_clock_info within a private
  * structure, obtaining a reference to it using container_of().
  *
@@ -189,6 +196,7 @@ struct ptp_clock_info {
 	int n_ext_ts;
 	int n_per_out;
 	int n_pins;
+	int n_per_lp;
 	int pps;
 	unsigned int supported_perout_flags;
 	unsigned int supported_extts_flags;
@@ -213,6 +221,8 @@ struct ptp_clock_info {
 	int (*verify)(struct ptp_clock_info *ptp, unsigned int pin,
 		      enum ptp_pin_function func, unsigned int chan);
 	long (*do_aux_work)(struct ptp_clock_info *ptp);
+	int (*perout_loopback)(struct ptp_clock_info *ptp, unsigned int index,
+			       int on);
 };
 
 struct ptp_clock;
-- 
2.34.1