netdev - Re: [net-next 03/15] net/mlx5: Add adjphase function to support hardware-only offset control

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Date:   Tue, 24 Jan 2023 12:33:05 +0200
From:   Bar Shapira <bar.shapira.work@...il.com>
To:     Richard Cochran <richardcochran@...il.com>,
        Rahul Rameshbabu <rrameshbabu@...dia.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>,
        Gal Pressman <gal@...dia.com>,
        Vincent Cheng <vincent.cheng.xh@...esas.com>
Subject: Re: [net-next 03/15] net/mlx5: Add adjphase function to support
 hardware-only offset control



On 24/01/2023 0:36, Richard Cochran wrote:
> On Mon, Jan 23, 2023 at 10:44:35AM -0800, Rahul Rameshbabu wrote:
> 
>> 1. Can the PHC servo change the frequency and not be expected to reset
>>     it back to the frequency before the phase control word is issued? If
>>     it's an expectation for the phase control word to reset the frequency
>>     back, I think that needs to be updated in the comments as a
>>     requirement.
> 
> I would expect the PHC to restore the previously dialed frequency once
> the ADJ_OFFSET (adjphase) calls stop.
> 

Hi Richard,
I guess this expectation should be part of the documentation too, right? 
Are there more expectations when calling adjphase?
In previous responses on the mailing list it said that adjphase should 
not cause the time to 'jump' - is it also correct?

It seems that "Feeds the given phase offset into the hardware clock's 
servo" is still missing some information.
Can you help clarify the expected result after calling adjphase from SW?

Thanks,
Bar

> Thanks,
> Richard