netdev - Re: [PATCH net 1/4] igc: Report speed and duplex as unknown when device is runtime suspended

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Message-ID: <20210129222255.5e7115bd@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 29 Jan 2021 22:22:55 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Tony Nguyen <anthony.l.nguyen@...el.com>
Cc:     davem@...emloft.net, Kai-Heng Feng <kai.heng.feng@...onical.com>,
        netdev@...r.kernel.org, sassmann@...hat.com,
        Sasha Neftin <sasha.neftin@...el.com>
Subject: Re: [PATCH net 1/4] igc: Report speed and duplex as unknown when
 device is runtime suspended

On Thu, 28 Jan 2021 13:38:48 -0800 Tony Nguyen wrote:
> From: Kai-Heng Feng <kai.heng.feng@...onical.com>
> 
> Similar to commit 165ae7a8feb5 ("igb: Report speed and duplex as unknown
> when device is runtime suspended"), if we try to read speed and duplex
> sysfs while the device is runtime suspended, igc will complain and
> stops working:

> The more generic approach will be wrap get_link_ksettings() with begin()
> and complete() callbacks, and calls runtime resume and runtime suspend
> routine respectively. However, igc is like igb, runtime resume routine
> uses rtnl_lock() which upper ethtool layer also uses.
> 
> So to prevent a deadlock on rtnl, take a different approach, use
> pm_runtime_suspended() to avoid reading register while device is runtime
> suspended.

Is someone working on the full fix to how PM operates?

There is another rd32(IGC_STATUS) in this file which I don't think 
is protected either.