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

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Message-ID: <Y88MqqbnUE6JWP3k@hoboy.vegasvil.org>
Date:   Mon, 23 Jan 2023 14:39:38 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     Rahul Rameshbabu <rrameshbabu@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        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 Mon, Jan 23, 2023 at 11:13:35AM -0800, Jacob Keller 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.
> 
> 
> My understanding from what Richard said is that .adjphase basically
> offloads the entire servo and corrections to the hardware, and thus
> would become responsible for maintaining the phase correction long term,
> and callers would not use both .adjphase at the same time as .adjtime or
> .adjfine

Right.

> > 2. Is it expected that a PHC servo implementation has a fixed
> >    configuration? In userspace servo implementations, configuration
> >    parameters are supported. Would we need devlink parameters to support
> >    configuring a PHC servo?
> > 
> 
> I would assume some sort of parameter configuration, either via devlink
> or something in the ptp_clock ecosystem if we get a device that has such
> configuration?

Yeah, but so far no one has asked for this.

Could also be debugfs if no commonality between hardware exists.

Thanks,
Richard