linux-kernel - Re: [PATCHv4 net-next] ptp/ioctl: support MONOTONIC_RAW timestamps for PTP_SYS_OFFSET

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Date: Wed, 08 May 2024 09:38:58 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Richard Cochran <richardcochran@...il.com>, Mahesh Bandewar
 <maheshb@...gle.com>
Cc: Netdev <netdev@...r.kernel.org>, Linux <linux-kernel@...r.kernel.org>,
 David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Arnd
 Bergmann <arnd@...db.de>, Sagi Maimon <maimon.sagi@...il.com>, Jonathan
 Corbet <corbet@....net>, John Stultz <jstultz@...gle.com>, Mahesh Bandewar
 <mahesh@...dewar.net>
Subject: Re: [PATCHv4 net-next] ptp/ioctl: support MONOTONIC_RAW timestamps
 for PTP_SYS_OFFSET_EXTENDED

On Tue, May 07 2024 at 21:44, Richard Cochran wrote:
> On Thu, May 02, 2024 at 02:10:47PM -0700, Mahesh Bandewar wrote:
>> +/*
>> + * ptp_sys_offset_extended - data structure for IOCTL operation
>> + *			     PTP_SYS_OFFSET_EXTENDED
>> + *
>> + * @n_samples:	Desired number of measurements.
>> + * @clockid:	clockid of a clock-base used for pre/post timestamps.
>> + * @rsv:	Reserved for future use.
>> + * @ts:		Array of samples in the form [pre-TS, PHC, post-TS]. The
>> + *		kernel provides @n_samples.
>> + *
>> + * History:
>> + * v1: Initial implementation.
>> + *
>> + * v2: Use the first word of the reserved-field for @clockid. That's
>> + *     backward compatible since v1 expects all three reserved words
>> + *     (@rsv[3]) to be 0 while the clockid (first word in v2) for
>> + *     CLOCK_REALTIME is '0'.
>
> This is not really appropriate for a source code comment.  The
> un-merged patch series iterations are preserved at lore.kernel in case
> someone needs that.
>
> The "backward compatible" information really wants to be in the commit
> message.

I agree that it wants to be in the commit message, but having the
version information in the kernel-doc which describes the UAPI is
sensible and useful. That's where I'd look first and asking a user to
dig up this information on lore is not really helpful.

Thanks,

        tglx