RE: [PATCH] net: lan743x_ptp: convert to ktime_get_clocktai_ts64

From: <Bryan.Whitehead@microchip.com>
To: <arnd@arndb.de>
Cc: <UNGLinuxDriver@MicrochipTechnology.Mail.Onmicrosoft.com>,
	<davem@davemloft.net>, <yuehaibing@huawei.com>,
	<netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] net: lan743x_ptp: convert to ktime_get_clocktai_ts64
Date: Wed, 15 Aug 2018 20:41:23 +0000	[thread overview]
Message-ID: <90A7E81AE28BAE4CBDDB3B35F187D2644073EA26@CHN-SV-EXMX02.mchp-main.com> (raw)
In-Reply-To: <CAK8P3a0f38ev5E4Zvg_3BS+1UN2NzYSw+dyRHXDwLCWgREXJ6g@mail.gmail.com>

> > > 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