ptp: add debugfs interfaces to loop back the periodic output signal

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>
Link: https://patch.msgid.link/20250905030711.1509648-2-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 69 insertions, 0 deletions

diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index 5739a57958c7..1d920f8e20a8 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -248,6 +248,69 @@ 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;
+	unsigned int index, enable;
+	int len, cnt, err;
+	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 %u", &index, &enable);
+	if (cnt != 2)
+		return -EINVAL;
+
+	if (index >= ops->n_per_lp)
+		return -EINVAL;
+
+	if (enable != 0 && enable != 1)
+		return -EINVAL;
+
+	err = ops->perout_loopback(ops, index, enable);
+	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 +452,12 @@ 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;