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Date:   Mon, 6 Jun 2022 14:42:56 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Tan Tee Min <tee.min.tan@...ux.intel.com>
Cc:     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>, Dan Murphy <dmurphy@...com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Voon Wei Feng <weifeng.voon@...el.com>,
        Sit Michael Wei Hong <michael.wei.hong.sit@...el.com>,
        Ling Pei Lee <pei.lee.ling@...el.com>,
        Looi Hong Aun <hong.aun.looi@...el.com>,
        Wong Vee Khee <vee.khee.wong@...el.com>,
        Tan Tee Min <tee.min.tan@...el.com>
Subject: Re: [PATCH net-next v2 1/1] net: phy: dp83867: retrigger SGMII AN
 when link change

> Below is the HW structure for Intel mGbE controller with external PHY.
> The SERDES is located in the PHY IF in the diagram below and the EQoS
> MAC uses pcs-xpcs driver for SGMII interface.
> 
>     <-----------------GBE Controller---------->|<---External PHY chip--->
>     +----------+         +----+            +---+           +------------+
>     |   EQoS   | <-GMII->| DW | < ------ > |PHY| <-SGMII-> |External PHY|
>     |   MAC    |         |xPCS|            |IF |           |(TI DP83867)|
>     +----------+         +----+            +---+           +------------+
>            ^               ^                 ^                ^
>            |               |                 |                |
>            +---------------------MDIO-------------------------+
> 
> There are registers in the DW XPCS to read the SGMII AN status and
> it's showing the SGMII AN has not completed and link status is down.
> But TI PHY is showing SGMII AN is completed and the copper link is
> established.
> 
> FYI, the current pcs-xpcs driver is configuring C37 SGMII as MAC-side
> SGMII, so it's expecting to receive AN Tx Config from PHY about the
> link state change after C28 AN is completed between PHY and Link Partner.
> Here is the pcs-xpcs code for your reference:
> https://elixir.bootlin.com/linux/latest/source/drivers/net/pcs/pcs-xpcs.c#L725
> 
> We faced a similar issue on MaxLinear GPY PHY in the past.
> And, MaxLinear folks admitted the issue and implemented fixes/improvements
> in the GPY PHY Firmware to overcome the SGMII AN issue.
> Besides, they have also implemented this similar SW Workaround in their
> PHY driver code to cater for the old Firmware.
> Feel free to refer GPY driver code here:
> https://elixir.bootlin.com/linux/latest/source/drivers/net/phy/mxl-gpy.c#L222
> 
> Apart from TI and MaxLinear PHY, we've also tested the Marvell 88E2110 and
> 88E1512 PHY with the MAC/SERDES combination above, Marvell PHY is working
> fine without any issue.

Thanks for the additional details.

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

    Andrew

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