netdev - Re: [RFC 1/3] ptp: Implement timex esterror support

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Message-ID: <8562b135-900f-4e8c-991b-4315fde5f1a7@machnikowski.net>
Date: Thu, 15 Aug 2024 11:43:57 +0200
From: Maciek Machnikowski <maciek@...hnikowski.net>
To: Richard Cochran <richardcochran@...il.com>
Cc: netdev@...r.kernel.org, jacob.e.keller@...el.com, vadfed@...a.com,
 darinzon@...zon.com, kuba@...nel.org
Subject: Re: [RFC 1/3] ptp: Implement timex esterror support



On 15/08/2024 06:23, Richard Cochran wrote:
> On Tue, Aug 13, 2024 at 12:56:00PM +0000, Maciek Machnikowski wrote:
>> The Timex structure returned by the clock_adjtime() POSIX API allows
>> the clock to return the estimated error. Implement getesterror
>> and setesterror functions in the ptp_clock_info to enable drivers
>> to interact with the hardware to get the error information.
> 
> So this can be implemented in the PTP class layer directly.  No need
> for driver callbacks.
Not if there is no connection between PTP layer and the consumer of this
information (TimeCard that uses PPS from embedded GNSS receiver, or a
PTP stack running on the infrastructure function of the multi-host
adapter or a DPU)

>  
>> getesterror additionally implements returning hw_ts and sys_ts
>> to enable upper layers to estimate the maximum error of the clock
>> based on the last time of correction.
> 
> But where are the upper layers?
They will be used to calculate the estimate of maxerror - don't want to
implement an API just to change it in a next RFC

> 
>> This functionality is not
>> directly implemented in the clock_adjtime and will require
>> a separate interface in the future.
> 
> We don't add interfaces that have no users.
> 
> Thanks,
> Richard

Noted - I'll try to explain it better next time