netdev - Re: PHY reset may still be asserted during MDIO probe

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Message-ID: <20210709155444.GB22278@shell.armlinux.org.uk>
Date:   Fri, 9 Jul 2021 16:54:44 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: PHY reset may still be asserted during MDIO probe

On Fri, Jul 09, 2021 at 05:33:36PM +0200, Geert Uytterhoeven wrote:
> Hi all,
> 
> I'm investigating a network failure after kexec on the Renesas Koelsch
> and Salvator-XS development boards, using the sh-eth or ravb driver.

Personally, I've never liked the reset support at PHY device level due
to problems like the one you've identified here. I've tended to use the
bus-level reset in preference to the PHY-level reset, particularly
because when you have multiple PHYs on the bus all sharing a common
reset, it seems to be the most sensible approach - and I see a single
PHY as no different from multiple PHYs on the bus.

However, I can see the argument for using the PHY level, but as you
note, that can create chicken and egg issues. I'm not entirely sure
why we decide to hold a PHY in reset when we've found it but not
started to make use of it - we don't do that with other devices in
the system. Why are PHYs special?

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