Re: [Intel-wired-lan] [PATCH net-next 1/2] ptp: add control over HW timestamp latch point

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Arkadiusz,


Thank you for your patch.

Am 21.10.24 um 16:19 schrieb Arkadiusz Kubalewski:
> Currently HW support of PTP/timesync solutions in network PHY chips can be
> implemented with two different approaches, the timestamp maybe latched
> either at the beginning or after the Start of Frame Delimiter (SFD) [1].
> 
> Allow ptp device drivers to provide user with control over the HW
> timestamp latch point with ptp sysfs ABI.

Please describe, that it’s done using `/sys` filesystem.

How can this be tested?

> [1] https://www.ieee802.org/3/cx/public/april20/tse_3cx_01_0420.pdf
> 
> Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
> Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
> ---
>   Documentation/ABI/testing/sysfs-ptp | 12 ++++++++
>   drivers/ptp/ptp_sysfs.c             | 44 +++++++++++++++++++++++++++++
>   include/linux/ptp_clock_kernel.h    | 29 +++++++++++++++++++
>   3 files changed, 85 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-ptp b/Documentation/ABI/testing/sysfs-ptp
> index 9c317ac7c47a..a0d89e0fd72e 100644
> --- a/Documentation/ABI/testing/sysfs-ptp
> +++ b/Documentation/ABI/testing/sysfs-ptp
> @@ -140,3 +140,15 @@ Description:
>   		PPS events to the Linux PPS subsystem. To enable PPS
>   		events, write a "1" into the file. To disable events,
>   		write a "0" into the file.
> +
> +What:		/sys/class/ptp/ptp<N>/ts_point
> +Date:		October 2024
> +Contact:	Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
> +Description:
> +		This file provides control over the point in time in
> +		which the HW timestamp is latched. As specified in IEEE
> +		802.3cx, the latch point can be either at the beginning
> +		or after the end of Start of Frame Delimiter (SFD).
> +		Value "0" means the timestamp is latched at the
> +		beginning of the SFD. Value "1" means that timestamp is
> +		latched after the end of SFD.

Would it make sense to let it be configured by strings, so it’s clear, 
what the values mean?

1.  beginning_of_sfd
2.  end_of_sfd

> diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
> index 6b1b8f57cd95..7e9f6ef368b6 100644
> --- a/drivers/ptp/ptp_sysfs.c
> +++ b/drivers/ptp/ptp_sysfs.c
> @@ -28,6 +28,46 @@ static ssize_t max_phase_adjustment_show(struct device *dev,
>   }
>   static DEVICE_ATTR_RO(max_phase_adjustment);
>   
> +static ssize_t ts_point_show(struct device *dev, struct device_attribute *attr,
> +			     char *page)
> +{
> +	struct ptp_clock *ptp = dev_get_drvdata(dev);
> +	enum ptp_ts_point point;
> +	int err;
> +
> +	if (!ptp->info->get_ts_point)
> +		return -EOPNOTSUPP;
> +	err = ptp->info->get_ts_point(ptp->info, &point);
> +	if (err)
> +		return err;
> +
> +	return sysfs_emit(page, "%d\n", point);
> +}
> +
> +static ssize_t ts_point_store(struct device *dev, struct device_attribute *attr,
> +			      const char *buf, size_t count)
> +{
> +	struct ptp_clock *ptp = dev_get_drvdata(dev);
> +	enum ptp_ts_point point;
> +	int err;
> +	u8 val;
> +
> +	if (!ptp->info->set_ts_point)
> +		return -EOPNOTSUPP;
> +	if (kstrtou8(buf, 0, &val))
> +		return -EINVAL;
> +	if (val > PTP_TS_POINT_MAX)
> +		return -EINVAL;
> +	point = val;
> +
> +	err = ptp->info->set_ts_point(ptp->info, point);
> +	if (err)
> +		return err;
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(ts_point);
> +
>   #define PTP_SHOW_INT(name, var)						\
>   static ssize_t var##_show(struct device *dev,				\
>   			   struct device_attribute *attr, char *page)	\
> @@ -335,6 +375,7 @@ static struct attribute *ptp_attrs[] = {
>   	&dev_attr_pps_enable.attr,
>   	&dev_attr_n_vclocks.attr,
>   	&dev_attr_max_vclocks.attr,
> +	&dev_attr_ts_point.attr,
>   	NULL
>   };
>   
> @@ -363,6 +404,9 @@ static umode_t ptp_is_attribute_visible(struct kobject *kobj,
>   	} else if (attr == &dev_attr_max_phase_adjustment.attr) {
>   		if (!info->adjphase || !info->getmaxphase)
>   			mode = 0;
> +	} else if (attr == &dev_attr_ts_point.attr) {
> +		if (!info->get_ts_point && !info->set_ts_point)
> +			mode = 0;
>   	}
>   
>   	return mode;
> diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
> index c892d22ce0a7..921d6615bd39 100644
> --- a/include/linux/ptp_clock_kernel.h
> +++ b/include/linux/ptp_clock_kernel.h
> @@ -55,6 +55,23 @@ struct ptp_system_timestamp {
>   	clockid_t clockid;
>   };
>   
> +/**
> + * enum ptp_ts_point - possible timestamp latch points (IEEE 802.3cx)
> + * @PTP_TS_POINT_SFD:      timestamp latched at the beginning of sending Start

The alignment of the start of the description looks strange with the 
second line being further right.

> + *			   of Frame Delimiter (SFD)
> + * @PTP_TS_POINT_POST_SFD: timestamp latched after the end of sending Start
> + *			   of Frame Delimiter (SFD)
> + */
> +enum ptp_ts_point {
> +	PTP_TS_POINT_SFD,
> +	PTP_TS_POINT_POST_SFD,
> +
> +	/* private: */
> +	__PTP_TS_POINT_MAX
> +};
> +
> +#define PTP_TS_POINT_MAX (__PTP_TS_POINT_MAX - 1)
> +
>   /**
>    * struct ptp_clock_info - describes a PTP hardware clock
>    *
> @@ -159,6 +176,14 @@ struct ptp_system_timestamp {
>    *                scheduling time (>=0) or negative value in case further
>    *                scheduling is not required.
>    *
> + * @set_ts_point: Request change of timestamp latch point, as the timestamp
> + *                could be latched at the beginning or after the end of start
> + *                frame delimiter (SFD), as described in IEEE 802.3cx
> + *                specification.
> + *
> + * @get_ts_point: Obtain the timestamp measurement latch point, counterpart of
> + *                .set_ts_point() for getting currently configured value.
> + *
>    * Drivers should embed their ptp_clock_info within a private
>    * structure, obtaining a reference to it using container_of().
>    *
> @@ -195,6 +220,10 @@ 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 (*set_ts_point)(struct ptp_clock_info *ptp,
> +			    enum ptp_ts_point point);
> +	int (*get_ts_point)(struct ptp_clock_info *ptp,
> +			    enum ptp_ts_point *point);
>   };
>   
>   struct ptp_clock;


Kind regards,

Paul