linux-kernel - Re: [PATCH RFT] ravb: Mask PHY mode to avoid inserting delays twice

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Message-ID: <ca3b597d-7593-0459-b7be-101f868317cf@cogentembedded.com>
Date:   Sun, 31 May 2020 20:30:55 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     David Miller <davem@...emloft.net>, geert+renesas@...der.be
Cc:     kuba@...nel.org, andrew@...n.ch, linux@...pel-privat.de,
        philippe.schenker@...adex.com, f.fainelli@...il.com,
        hkallweit1@...il.com, linux@...linux.org.uk,
        kazuya.mizuguchi.ks@...esas.com, grygorii.strashko@...com,
        wsa+renesas@...g-engineering.com, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFT] ravb: Mask PHY mode to avoid inserting delays twice

Hello!

On 31.05.2020 7:51, David Miller wrote:

>> Until recently, the Micrel KSZ9031 PHY driver ignored any PHY mode
>> ("RGMII-*ID") settings, but used the hardware defaults, augmented by
>> explicit configuration of individual skew values using the "*-skew-ps"
>> DT properties.  The lack of PHY mode support was compensated by the
>> EtherAVB MAC driver, which configures TX and/or RX internal delay
>> itself, based on the PHY mode.
>>
>> However, now the KSZ9031 driver has gained PHY mode support, delays may
>> be configured twice, causing regressions.  E.g. on the Renesas
>> Salvator-X board with R-Car M3-W ES1.0, TX performance dropped from ca.
>> 400 Mbps to 0.1-0.3 Mbps, as measured by nuttcp.
>>
>> As internal delay configuration supported by the KSZ9031 PHY is too
>> limited for some use cases, the ability to configure MAC internal delay
>> is deemed useful and necessary.  Hence a proper fix would involve
>> splitting internal delay configuration in two parts, one for the PHY,
>> and one for the MAC.  However, this would require adding new DT
>> properties, thus breaking DTB backwards-compatibility.
>>
>> Hence fix the regression in a backwards-compatibility way, by letting
>> the EtherAVB driver mask the PHY mode when it has inserted a delay, to
>> avoid the PHY driver adding a second delay.  This also fixes messages
>> like:
>>
>>      Micrel KSZ9031 Gigabit PHY e6800000.ethernet-ffffffff:00: *-skew-ps values should be used only with phy-mode = "rgmii"
>>
>> as the PHY no longer sees the original RGMII-*ID mode.
>>
>> Solving the issue by splitting configuration in two parts can be handled
>> in future patches, and would require retaining a backwards-compatibility
>> mode anyway.
>>
>> Fixes: bcf3440c6dd78bfe ("net: phy: micrel: add phy-mode support for the KSZ9031 PHY")
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> 
> Applied to net-next, thank you.

    Why not to net.git? It's a fix after all...

MBR, Sergei