linux-kernel - Re: signal quality and cable diagnostic

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Message-ID: <20200512064858.GA16536@pengutronix.de>
Date:   Tue, 12 May 2020 08:48:58 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Marek Vasut <marex@...x.de>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jonathan Corbet <corbet@....net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        mkl@...gutronix.de, kernel@...gutronix.de,
        David Jander <david@...tonic.nl>,
        Jakub Kicinski <kuba@...nel.org>,
        Christian Herber <christian.herber@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: signal quality and cable diagnostic

On Mon, May 11, 2020 at 04:59:26PM +0200, Michal Kubecek wrote:
> On Mon, May 11, 2020 at 04:13:10PM +0200, Oleksij Rempel wrote:
> > 
> > I continue to work on TJA11xx PHY and need to export some additional
> > cable diagnostic/link stability information: Signal Quality Index (SQI).
> > The PHY data sheet describes it as following [1]:
> > ================================================================================
> >   6.10.3   Link stability
> > 
> > The signal-to-noise ratio is the parameter used to estimate link
> > stability. The PMA Receive function monitors the signal-to-noise ratio
> > continuously. Once the signal-to-noise ratio falls below a configurable
> > threshold (SQI_FAILLIMIT), the link status is set to FAIL and
> > communication is interrupted. The TJA1100 allows for adjusting the
> > sensitivity of the PMA Receive function by configuring this threshold.
> > The microcontroller can always check the current value of the
> > signal-to-noise ratio via the SMI, allowing it to track a possible
> > degradation in link stability.
> > ================================================================================
> > 
> > Since this functionality is present at least on TJA11xx PHYs and
> > mandatory according to Open Alliance[2], I hope this functionality is
> > present on other 100/1000Base-T1 PHYs. So may be some common abstraction
> > is possible. What would be the best place to provide it for the user
> > space? According to the [2] SQI, is the part of Dynamic Channel Quality
> > (DCQ) together with Mean Square Error (MSE) and Peak MSE value (pMSE).
> 
> IIUC these would be read-only parameters describing current state of the
> link which can be queried at any time. If this is the case, adding them
> as attributes to ETHTOOL_MSG_LINKSTATE_GET_REPLY message seems most
> fitting.

ok

> As for getting / setting the threshold, perhaps ETHTOOL_MSG_LINKINFO_GET
> and ETHTOOL_MSG_LINKINFO_SET. Unless you expect more configurable
> parameters like this in which case we may want to consider adding new
> request type (e.g. link params or link management).

Currently in my short term todo are:
- SQI
- PHY undervoltage
- PHY overtemerature

So far, I have no idea for PHY health diagnostic.

If we consider at least the  mandatory properties listed in the opensig, then
we would get following list:

- DCQ (dynamic channel group)
  - SQI (Signal Quality Index)
- HDD (Harness defect detection group)
  - OS (Open/Short detection) ----------------- implemented, cable test
    request.
- LQ (Link Quality)
  - LTT (Link-training time. The time of the last link training)
  - LFL (Link Failures and Losses. Number of link losses since the last
    power cycle)
  - COM (communication ready) ----------------- implemented?
- POL (Polarity detection & correction)
  - DET (Polarity detect)

I personally would add RE_ERR counter in this list as well.

Probably some one, soon or later, will try to implement them.

If I see it correctly, some of this properties are already implemented
within other request types. Is it worth to a add a new request type for
the rest of them?

Regards,
Oleksij

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