Re: [PATCH v6 net-next 04/17] ptp: add debugfs interfaces to loop back the periodic output signal

[Frank Li <Frank.li@nxp.com>]

On Wed, Aug 27, 2025 at 02:33:19PM +0800, Wei Fang wrote:
> 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

Genernally sys interface only 1 input for each entry.

I suggest create one file for each channel.

/sys/kernel/debug/ptp<N>/perout<m>_loopback_enable

echo 1 > /sys/kernel/debug/ptp<N>/perout<m>_loopback_enable

Frank

>
> 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>
>
> ---
> v6 changes:
> 1. New patch
> ---
>  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 2b0fd62a17ef..0a45c5ebd904 100644
> --- a/drivers/ptp/ptp_clock.c
> +++ b/drivers/ptp/ptp_clock.c
> @@ -237,6 +237,66 @@ 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,
> @@ -378,6 +438,12 @@ 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
>