netdev - Re: [PATCH net 1/2] net: phylink: Force link down and retrigger resolve on interface change

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Date:   Tue, 23 Nov 2021 11:20:59 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Andrew Lunn <andrew@...n.ch>, davem@...emloft.net
Subject: Re: [PATCH net 1/2] net: phylink: Force link down and retrigger
 resolve on interface change

On Tue, Nov 23, 2021 at 12:51:53AM +0100, Marek Behún wrote:
> On PHY state change the phylink_resolve() function can read stale
> information from the MAC and report incorrect link speed and duplex to
> the kernel message log.
> 
> Example with a Marvell 88X3310 PHY connected to a SerDes port on Marvell
> 88E6393X switch:
> - PHY driver triggers state change due to PHY interface mode being
>   changed from 10gbase-r to 2500base-x due to copper change in speed
>   from 10Gbps to 2.5Gbps, but the PHY itself either hasn't yet changed
>   its interface to the host, or the interrupt about loss of SerDes link
>   hadn't arrived yet (there can be a delay of several milliseconds for
>   this), so we still think that the 10gbase-r mode is up
> - phylink_resolve()
>   - phylink_mac_pcs_get_state()
>     - this fills in speed=10g link=up
>   - interface mode is updated to 2500base-x but speed is left at 10Gbps
>   - phylink_major_config()
>     - interface is changed to 2500base-x
>   - phylink_link_up()
>     - mv88e6xxx_mac_link_up()
>       - .port_set_speed_duplex()
>         - speed is set to 10Gbps
>     - reports "Link is Up - 10Gbps/Full" to dmesg
> 
> Afterwards when the interrupt finally arrives for mv88e6xxx, another
> resolve is forced in which we get the correct speed from
> phylink_mac_pcs_get_state(), but since the interface is not being
> changed anymore, we don't call phylink_major_config() but only
> phylink_mac_config(), which does not set speed/duplex anymore.
> 
> To fix this, we need to force the link down and trigger another resolve
> on PHY interface change event.
> 
> Fixes: 9525ae83959b ("phylink: add phylink infrastructure")
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> Signed-off-by: Marek Behún <kabel@...nel.org>

I'm pretty sure someone will highlight that the author of the patch
should be the first sign-off - which doesn't match given the way
you've sent this patch. That probably needs fixing before it's
applied.

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