linux-kernel - Re: [RFC PATCH net 0/2] Make phylink and DSA wait for PHY driver that defers probe

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Date:   Thu, 19 May 2022 17:32:35 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        John Stultz <jstultz@...gle.com>,
        Alvin ┼áipraga <alsi@...g-olufsen.dk>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [RFC PATCH net 0/2] Make phylink and DSA wait for PHY driver
 that defers probe

> > There is a very different approach, which might be simpler.
> > 
> > We know polling will always work. And it should be possible to
> > transition between polling and interrupt at any point, so long as the
> > phylock is held. So if you get -EPROBE_DEFFER during probe, mark some
> > state in phydev that there should be an irq, but it is not around yet.
> > When the phy is started, and phylib starts polling, look for the state
> > and try getting the IRQ again. If successful, swap to interrupts, if
> > not, keep polling. Maybe after 60 seconds of polling and trying, give
> > up trying to find the irq and stick with polling.
> 
> That doesn't sound like something that I'd backport to stable kernels.

> What motivates me to make these changes in the first place is the idea
> that current kernels should work with updated device trees.

By current, you mean old kernels, LTS etc. You want an LTS kernel to
work with a new DT blob? You want forward compatibility with a DT
blob. Do the stable rules say anything about that?

      Andrew