netdev - Re: [PATCH net-next v2 1/6] net: dsa: add support for phylink mac_select

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Date:   Mon, 21 Feb 2022 14:44:34 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Ansuel Smith <ansuelsmth@...il.com>, Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH net-next v2 1/6] net: dsa: add support for phylink
 mac_select_pcs()

On Mon, Feb 21, 2022 at 04:32:54PM +0200, Vladimir Oltean wrote:
> Alternatively, phylink_create() gets the initial PHY interface mode
> passed to it, I wonder, couldn't we call mac_select_pcs() with that in
> order to determine whether the function is a stub or not?

That would be rather prone to odd behaviour depending on how
phylink_create() is called, depending on the initial interface mode.
If the initial interface mode causes mac_select_pcs() to return NULL
but it actually needed to return a PCS for a different interface mode,
then we fail.

> *and as I haven't considered, to be honest. When phylink_major_config()
> gets called after a SGMII to 10GBaseR switchover, and mac_select_pcs is
> called and returns NULL, the current behavior is to keep working with
> the PCS for SGMII. Is that intended?

It was not originally intended, but as a result of the discussion
around this patch which didn't go anywhere useful, I dropped it as
a means to a path of least resistance.

https://patchwork.kernel.org/project/linux-arm-kernel/patch/E1mpSba-00BXp6-9e@rmk-PC.armlinux.org.uk/

-- 
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