netdev - Re: [PATCH v4 1/2] ethtool: implement Energy Detect Powerdown support via phy-tunable

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Date:   Sat, 14 Sep 2019 17:26:14 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        robh+dt@...nel.org, mark.rutland@....com, f.fainelli@...il.com,
        hkallweit1@...il.com, mkubecek@...e.cz
Subject: Re: [PATCH v4 1/2] ethtool: implement Energy Detect Powerdown
 support via phy-tunable

On Thu, Sep 12, 2019 at 07:28:11PM +0300, Alexandru Ardelean wrote:
> The `phy_tunable_id` has been named `ETHTOOL_PHY_EDPD` since it looks like
> this feature is common across other PHYs (like EEE), and defining
> `ETHTOOL_PHY_ENERGY_DETECT_POWER_DOWN` seems too long.
> 
> The way EDPD works, is that the RX block is put to a lower power mode,
> except for link-pulse detection circuits. The TX block is also put to low
> power mode, but the PHY wakes-up periodically to send link pulses, to avoid
> lock-ups in case the other side is also in EDPD mode.
> 
> Currently, there are 2 PHY drivers that look like they could use this new
> PHY tunable feature: the `adin` && `micrel` PHYs.
> 
> The ADIN's datasheet mentions that TX pulses are at intervals of 1 second
> default each, and they can be disabled. For the Micrel KSZ9031 PHY, the
> datasheet does not mention whether they can be disabled, but mentions that
> they can modified.
> 
> The way this change is structured, is similar to the PHY tunable downshift
> control:
> * a `ETHTOOL_PHY_EDPD_DFLT_TX_MSECS` value is exposed to cover a default
>   TX interval; some PHYs could specify a certain value that makes sense
> * `ETHTOOL_PHY_EDPD_NO_TX` would disable TX when EDPD is enabled
> * `ETHTOOL_PHY_EDPD_DISABLE` will disable EDPD
> 
> As noted by the `ETHTOOL_PHY_EDPD_DFLT_TX_MSECS` the interval unit is 1
> millisecond, which should cover a reasonable range of intervals:
>  - from 1 millisecond, which does not sound like much of a power-saver
>  - to ~65 seconds which is quite a lot to wait for a link to come up when
>    plugging a cable
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew