netdev - Re: mvpp2 switch from gmac to xlg requires ifdown/ifup

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Message-ID: <20210723080538.GB22278@shell.armlinux.org.uk>
Date:   Fri, 23 Jul 2021 09:05:38 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org
Subject: Re: mvpp2 switch from gmac to xlg requires ifdown/ifup

On Fri, Jul 23, 2021 at 03:52:02AM +0200, Marek Behún wrote:
> Hello Russell (and possibly others),
> 
> I discovered that with mvpp2 when switching from gmac (sgmii or
> 2500base-x mode) to xlg (10gbase-r mode) due to phylink requesting this
> change, the link won't come up unless I do
>   ifconfig ethX down
>   ifconfig ethX up
> 
> Can be reproduced on MacchiatoBIN:
> 1. connect the two 10g RJ-45 ports (88X3310 PHY) with one cable
> 2. bring the interfaces up
> 3. the PHYs should link in 10gbase-t, links on MACs will go up in
>    10gbase-r
> 4. use ethtool on one of the interfaces to advertise modes only up to
>    2500base-t
> 5. the PHYs will unlink and then link at 2.5gbase-t, links on MACs will
>    go up in 2500base-x
> 6. use ethtool on the same interface as in step 4 to advertise all
>    supported modes
> 
> 7. the PHYs will unlink and then link at 10gbase-t, BUT MACs won't link
>    !!!
> 8. execute
>      ifconfig ethX down ; ifconfig ethX up
>    on both interfaces. After this, the MACs will successfully link in
>    10gbase-r with the PHYs
> 
> It seems that the mvpp2 driver code needs to make additional stuff when
> chaning mode from gmac to xlg. I haven't yet been able to find out
> what, though.
> 
> BTW I discovered this because I am working on adding support for
> 5gbase-r mode to mvpp2, so that the PHY can support 5gbase-t on copper
> side.
> The ifdown/ifup cycle is required when switching from gmac to xlg, i.e.:
> 	sgmii		to	5gbase-r
> 	sgmii		to	10gbase-r
> 	2500base-x	to	5gbase-r
> 	2500base-x	to	10gbase-r
> but also when switching from xlg to different xlg:
> 	5gbase-r	to	10gbase-r
> 	10gbase-r	to	5gbase-r
> 
> Did someone notice this bug? I see that Russell made some changes in
> the phylink pcs API that touched mvpp2 (the .mac_config method got
> split into .mac_prepare, .mac_config and .mac_finish, and also some
> other changes). I haven't tried yet if the switch from gmac to xlg
> worked at some time in the past. But if it did, maybe these changes
> could be the cause?

What are the PHY leds doing when you encounter this bug?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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