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. Provide a new file under sysfs
ptp device (/sys/class/ptp/ptp<N>/ts_point). The file is available for the
user, if the device driver implements at least one of newly provided
callbacks. If the file is not provided the user shall find a PHY timestamp
latch point within the HW vendor specification.

The file is designed for root user/group access only, as the read for
regular user could impact performance of the ptp device.

Usage, examples:

** Obtain current state:
$ cat /sys/class/ptp/ptp<N>/ts_point
Command returns enum/integer:
* 0 - timestamp latched by PHY at the beginning of SFD,
* 1 - timestamp latched by PHY after the SFD,
* None - callback returns error to the user.

** Configure timestamp latch point at the beginning of SFD:
$ echo 0 > /sys/class/ptp/ptp<N>/ts_point

** Configure timestamp latch point after the SFD:
$ echo 1 > /sys/class/ptp/ptp<N>/ts_point

[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>
---
v2:
- improve commit message, describe the new sysfs file and add usage
  examples,
- improve alignment in documentation of enum ptp_ts_point,
- use 0660 permission for ts_point file.
---
 Documentation/ABI/testing/sysfs-ptp | 12 ++++++++
 drivers/ptp/ptp_sysfs.c             | 44 +++++++++++++++++++++++++++++
 include/linux/ptp_clock_kernel.h    | 30 ++++++++++++++++++++
 3 files changed, 86 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.
diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
index 6b1b8f57cd95..76c2fac54be4 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(ts_point, 0660, ts_point_show, ts_point_store);
+
 #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..ea1bcca7f7f6 100644
--- a/include/linux/ptp_clock_kernel.h
+++ b/include/linux/ptp_clock_kernel.h
@@ -55,6 +55,24 @@ 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
+ *		      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 +177,14 @@ 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 +221,10 @@ 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;
-- 
2.38.1

On 10/28/24 21:47, Arkadiusz Kubalewski wrote:
> 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. Provide a new file under sysfs
> ptp device (/sys/class/ptp/ptp<N>/ts_point). The file is available for the
> user, if the device driver implements at least one of newly provided
> callbacks. If the file is not provided the user shall find a PHY timestamp
> latch point within the HW vendor specification.
> 
> The file is designed for root user/group access only, as the read for
> regular user could impact performance of the ptp device.
> 
> Usage, examples:
> 
> ** Obtain current state:
> $ cat /sys/class/ptp/ptp<N>/ts_point
> Command returns enum/integer:
> * 0 - timestamp latched by PHY at the beginning of SFD,
> * 1 - timestamp latched by PHY after the SFD,
> * None - callback returns error to the user.
> 
> ** Configure timestamp latch point at the beginning of SFD:
> $ echo 0 > /sys/class/ptp/ptp<N>/ts_point
> 
> ** Configure timestamp latch point after the SFD:
> $ echo 1 > /sys/class/ptp/ptp<N>/ts_point
> 
> [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>

[...]

> diff --git a/include/linux/ptp_clock_kernel.h b/include/linux/ptp_clock_kernel.h
> index c892d22ce0a7..ea1bcca7f7f6 100644
> --- a/include/linux/ptp_clock_kernel.h
> +++ b/include/linux/ptp_clock_kernel.h
> @@ -55,6 +55,24 @@ 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
> + *		      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)

I would move PTP_TS_POINT_MAX into the enum

>From: Kitszel, Przemyslaw <przemyslaw.kitszel@intel.com>
>Sent: Tuesday, October 29, 2024 9:25 AM
>Subject: Re: [PATCH net-next v2 1/2] ptp: add control over HW timestamp
>latch point
>
>On 10/28/24 21:47, Arkadiusz Kubalewski wrote:
>> 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. Provide a new file under
>> sysfs ptp device (/sys/class/ptp/ptp<N>/ts_point). The file is
>> available for the user, if the device driver implements at least one
>> of newly provided callbacks. If the file is not provided the user
>> shall find a PHY timestamp latch point within the HW vendor
>>specification.
>>
>> The file is designed for root user/group access only, as the read for
>> regular user could impact performance of the ptp device.
>>
>> Usage, examples:
>>
>> ** Obtain current state:
>> $ cat /sys/class/ptp/ptp<N>/ts_point
>> Command returns enum/integer:
>> * 0 - timestamp latched by PHY at the beginning of SFD,
>> * 1 - timestamp latched by PHY after the SFD,
>> * None - callback returns error to the user.
>>
>> ** Configure timestamp latch point at the beginning of SFD:
>> $ echo 0 > /sys/class/ptp/ptp<N>/ts_point
>>
>> ** Configure timestamp latch point after the SFD:
>> $ echo 1 > /sys/class/ptp/ptp<N>/ts_point
>>
>> [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>
>
>[...]
>
>> diff --git a/include/linux/ptp_clock_kernel.h
>> b/include/linux/ptp_clock_kernel.h
>> index c892d22ce0a7..ea1bcca7f7f6 100644
>> --- a/include/linux/ptp_clock_kernel.h
>> +++ b/include/linux/ptp_clock_kernel.h
>> @@ -55,6 +55,24 @@ 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
>> + *		      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)
>
>I would move PTP_TS_POINT_MAX into the enum
>

Fixed in v3.

Thank you!
Arkadiusz