netdev - Re: [PATCH net] net: dsa: bcm_sf2: Prevent GPHY shutdown for kexec'd kernels

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Message-ID: <605285c4-bc92-0a0d-87b9-5066e39078a3@gmail.com>
Date:   Thu, 20 Oct 2016 11:47:53 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com
Subject: Re: [PATCH net] net: dsa: bcm_sf2: Prevent GPHY shutdown for kexec'd
 kernels

On 10/20/2016 11:44 AM, David Miller wrote:
> From: Florian Fainelli <f.fainelli@...il.com>
> Date: Thu, 20 Oct 2016 09:32:19 -0700
> 
>> For a kernel that is being kexec'd we re-enable the integrated GPHY in
>> order for the subsequent MDIO bus scan to succeed and properly bind to
>> the bcm7xxx PHY driver. If we did not do that, the GPHY would be shut
>> down by the time the MDIO driver is probing the bus, and it would fail
>> to read the correct PHY OUI and therefore bind to an appropriate PHY
>> driver. Later on, this would cause DSA not to be able to successfully
>> attach to the PHY, and the interface would not be created at all.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> 
> Applied, but I have to wonder...
> 
> If enabling the GPHY is necessary for proper probing, why isn't the
> kexec kernel enabling it properly?

The GPHY enable control is unfortunately located in the switch register
block space and is dependent upon the switch port to be
enabled/accessible, which the DSA layer won't create if the GPHY is not
successfully probed and bound to a PHY driver. It did not appear that
probe deferral could help solve that problem, since MDIO and switch are
reasonable independent from each other.

This was the easiest way I could come up with, without requiring DT
changes and references to register blocks that are not quite relevant to
each other.

HTH
-- 
Florian