linux-kernel - Re: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency values and timestamping check for LAN8814 phy

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Date:   Sun, 13 Mar 2022 13:03:22 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     "Allan W. Nielsen" <allan.nielsen@...rochip.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Woojung.Huh@...rochip.com,
        linux@...linux.org.uk, Horatiu.Vultur@...rochip.com,
        Divya.Koppera@...rochip.com, netdev@...r.kernel.org,
        hkallweit1@...il.com, davem@...emloft.net, kuba@...nel.org,
        robh+dt@...nel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, UNGLinuxDriver@...rochip.com,
        Madhuri.Sripada@...rochip.com, Manohar.Puri@...rochip.com
Subject: Re: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency
 values and timestamping check for LAN8814 phy

On Sun, Mar 13, 2022 at 08:37:44PM +0100, Allan W. Nielsen wrote:
> On Sun, Mar 13, 2022 at 04:07:24PM +0100, Andrew Lunn wrote:
> > On Sat, Mar 12, 2022 at 06:46:46PM -0800, Richard Cochran wrote:
> > > On Sat, Mar 12, 2022 at 09:04:31PM +0100, Andrew Lunn wrote:
> > > > Do these get passed to the kernel so the hardware can act on them, or
> > > > are they used purely in userspace by ptp4l?
> > >
> > > user space only.
> I'm wondering if one-step will work if these correction values are not
> applied to HW.

They are applied to the time stamps that are available to the
program.  So, no, they obviously won't be applied to one step Sync.
But then again, neither will the driver values.

(You could imagine a HW tstamp unit that includes a correction factor,
for example by adding the egress time stamp value to the correction
field.  But there are no APIs for that, and maybe no HW either.)

(BTW one step is overrated IMO)

Thanks,
Richard