netdev - Re: [PATCH] Revert "net: linkwatch: add check for netdevice being present to linkwatch_do

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Message-Id: <20200923.131529.637266321442993059.davem@davemloft.net>
Date:   Wed, 23 Sep 2020 13:15:29 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     hkallweit1@...il.com
Cc:     saeed@...nel.org, geert+renesas@...der.be, f.fainelli@...il.com,
        andrew@...n.ch, kuba@...nel.org, gaku.inami.xh@...esas.com,
        yoshihiro.shimoda.uh@...esas.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "net: linkwatch: add check for netdevice being
 present to linkwatch_do_dev"

From: Heiner Kallweit <hkallweit1@...il.com>
Date: Wed, 23 Sep 2020 21:58:59 +0200

> On 23.09.2020 20:35, Saeed Mahameed wrote:
>> Why would a driver detach the device on ndo_stop() ?
>> seems like this is the bug you need to be chasing ..
>> which driver is doing this ? 
>> 
> Some drivers set the device to PCI D3hot at the end of ndo_stop()
> to save power (using e.g. Runtime PM). Marking the device as detached
> makes clear to to the net core that the device isn't accessible any
> longer.

That being the case, the problem is that IFF_UP+!present is not a
valid netdev state.

Is it simply the issue that, upon resume, IFF_UP is marked true before
the device is brought out from D3hot state and thus marked as present
again?