linux-kernel - Re: [PATCH RFC V1 net-next 2/4] net: Expose available time stamping layers to user space.

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Message-ID: <YdOL5Dc19lSAGTuj@shell.armlinux.org.uk>
Date:   Mon, 3 Jan 2022 23:51:00 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        David Miller <davem@...emloft.net>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH RFC V1 net-next 2/4] net: Expose available time stamping
 layers to user space.

On Mon, Jan 03, 2022 at 03:25:53PM -0800, Richard Cochran wrote:
> Time stamping on network packets may happen either in the MAC or in
> the PHY, but not both.  In preparation for making the choice
> selectable, expose both the current and available layers via sysfs.
> 
> In accordance with the kernel implementation as it stands, the current
> layer will always read as "phy" when a PHY time stamping device is
> present.  Future patches will allow changing the current layer
> administratively.
> 
> Signed-off-by: Richard Cochran <richardcochran@...il.com>

Did you mean to introduce "selected_timestamping_layer" in this patch -
it appears to be a write only variable.

As it stands, it gets set to indicate PHY mode just by a network driver
binding to a PHY. If this gets used based on that decision to direct
where get_ts_info() goes, then this will break mvpp2 PTP.

I suggest that the introduction of "selected_timestamping_layer" is
moved to the patch where it's actually used for a better review.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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