Re: [PATCH net-next v2 1/1] net: phy: dp83867: retrigger SGMII AN when link change

[Andrew Lunn <andrew@lunn.ch>]

> 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@lunn.ch>

    Andrew