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

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Message-ID: <9b7ccd9e-fca3-4a72-806f-3e99ab5ae4bd@intel.com>
Date: Tue, 29 Oct 2024 09:24:39 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>
CC: <anthony.l.nguyen@...el.com>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<richardcochran@...il.com>, Aleksandr Loktionov
	<aleksandr.loktionov@...el.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>
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@...el.com>
> Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.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