netdev - Re: [PATCH] [RFC] net: phy: Fix reboot crash if CONFIG_IP

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Date:   Tue, 5 Jan 2021 15:10:13 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Ioana Ciornei <ioana.ciornei@....com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] net: phy: Fix reboot crash if CONFIG_IP_PNP is not
 set

> I added a statically-linked ethtool binary to my initramfs, and can
> confirm that retrieving the PHY statistics does not access the PHY
> registers when the device is suspended:
> 
>     # ethtool --phy-statistics eth0
>     no stats available
>     # ifconfig eth0 up
>     # ethtool --phy-statistics eth0
>     PHY statistics:
> 	 phy_receive_errors: 0
> 	 phy_idle_errors: 0
>     #
> 
> In the past, we've gone to great lengths to avoid accessing the PHY
> registers when the device is suspended, usually in the statistics
> handling (see e.g. [1][2]).

I would argue that is the wrong approach. The PHY device is a
device. It has its own lifetime. You would not suspend a PCI bus
controller without first suspending all PCI devices on the bus etc.

> +static int sh_mdiobb_read(struct mii_bus *bus, int phy, int reg)
> +{
> +	struct bb_info *bb = container_of(bus->priv, struct bb_info, ctrl);

mii_bus->parent should give you dev, so there is no need to add it to
bb_info.

> +	/* Wrap accessors with Runtime PM-aware ops */
> +	bitbang->read = mdp->mii_bus->read;
> +	bitbang->write = mdp->mii_bus->write;
> +	mdp->mii_bus->read = sh_mdiobb_read;
> +	mdp->mii_bus->write = sh_mdiobb_write;

I did wonder about just exporting the two functions so you can
directly call them.

Otherwise, this looks good.

	   Andrew