netdev - Re: [PATCH 3/4] net: macb: Add pm runtime support

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Date:   Wed, 31 Oct 2018 15:54:00 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Harini Katakam <harini.katakam@...inx.com>
Cc:     nicolas.ferre@...rochip.com, davem@...emloft.net,
        claudiu.beznea@...rochip.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, michal.simek@...inx.com,
        harinikatakamlinux@...il.com, Harini Katakam <harinik@...inx.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>
Subject: Re: [PATCH 3/4] net: macb: Add pm runtime support

On Wed, Oct 31, 2018 at 09:10:22AM +0530, Harini Katakam wrote:
> From: Harini Katakam <harinik@...inx.com>
> 
> Add runtime pm functions and move clock handling there.
> If device is suspended and not a wake device, then return from
> mdio read/write functions without performing any action because
> the clocks are not active.
> 
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>
> Signed-off-by: Harini Katakam <harinik@...inx.com>
> ---
> Changes from RFC:
> Updated pm get sync/put sync calls.
> Removed unecessary clk up in mdio helpers.

This last bit has me worried.

The MDIO bus is a shared bus with a life of its own.  You can have
multiple PHYs and switches on it. The PHYs can for a different
Ethernet MAC. Switch drivers will expect to be able to address the
switch when the interface is down.

The FEC driver did something similar for a while. I had to make MDIO
read/write runtime PM aware, otherwise i could not access the Ethernet
switch hanging of its MDIO bus.

	Andrew