RE: [PATCH net-next v2 1/2] ptp: add control over HW timestamp latch point

[Kubalewski, Arkadiusz]

>From: Kitszel, Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>
>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@xxxxxxxxx>
>> Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@xxxxxxxxx>
>
>[...]
>
>> 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