linux-kernel - RE: [PATCH] net: lan743x_ptp: convert to ktime_get_clocktai

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Message-ID: <90A7E81AE28BAE4CBDDB3B35F187D2644073EA26@CHN-SV-EXMX02.mchp-main.com>
Date:   Wed, 15 Aug 2018 20:41:23 +0000
From:   <Bryan.Whitehead@...rochip.com>
To:     <arnd@...db.de>
CC:     <UNGLinuxDriver@...rochipTechnology.Mail.Onmicrosoft.com>,
        <davem@...emloft.net>, <yuehaibing@...wei.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net: lan743x_ptp: convert to ktime_get_clocktai_ts64

> > > Question: this is the only ptp driver that sets the hardware time to
> > > the current system time in TAI. Why does it do that?
> >
> > This is done when the driver starts up after reset. Otherwise the clock is off
> by 48 years.
> > It seemed to me that the system time was the most appropriate clock to
> sync to.
> > If my reasoning is incorrect, please enlighten me.
> 
> I've never worked with PTP, but my understanding from looking at the other
> drivers is that the time normally gets set either from another host through
> the PTP protocol, or using clock_settime() from user space with the current
> time.

Those methods will still work. But if it's not set by those methods, I thought the clock should at least be set once on driver startup to align with the system clock. After that, other methods are free to reset it again.

Bryan