netdev - Re: [PATCH net-next v6 2/3] net: phy: broadcom: Add PTP support for some Broadcom PHYs.

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Message-ID: <85F4D27D-EF7F-4F69-9020-769D2461777D@gmail.com>
Date:   Thu, 09 Jun 2022 12:21:25 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     netdev@...r.kernel.org, kernel-team@...com,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Lasse Johnsen <l@...johnsen.me>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH net-next v6 2/3] net: phy: broadcom: Add PTP support for some Broadcom PHYs.

On 8 Jun 2022, at 21:01, Richard Cochran wrote:

> On Wed, Jun 08, 2022 at 02:29:15PM -0700, Jonathan Lemon wrote:
>> Do you have a stress test to verify one way or the other?
>
> You can set a large freq. offset on the server.  For example
>
>    phc_ctl eth0 -- freq 500000
>
> for 500 ppm and see what the client does.

Server:
  phc_ctl /dev/ptp0 -- freq 60000000

Client (cm4):
  ptp4l[252648.584]: rms    5 max    5 freq -59995478 +/-   5
  ptp4l[252649.584]: rms    2 max    2 freq -59995476 +/-   1 delay   165 +/-   0
  ptp4l[252650.585]: rms    3 max    3 freq -59995475 +/-   1 delay   165 +/-   0

Flipping client and server roles still works, (up to the 62499999 limit
for the igb adapter I'm using on the other end of the cm4 link.)


Looking at the math, the adjustment in bcm_ptp_adjfine() can be up to
0x7fffffff, as this is added to a 0x8000000 base.

So:
  (0x7fffffff * 15625) >> 9 == 65535999969 scaled ppm

  (65535999969 * 125) >> 13 == 999999999 ppb

Seems like the 100000000 ppb max value is in range?
-- 
Jonathan