linux-kernel - Re: [PATCH v2 2/2] net-sysfs: Ensure begin/complete are called in speed_show() and duplex

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Date:   Wed, 5 Feb 2020 10:23:45 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>, davem@...emloft.ne,
        jeffrey.t.kirsher@...el.com,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ido Schimmel <idosch@...lanox.com>,
        Jouni Hogander <jouni.hogander@...kie.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Wang Hai <wanghai26@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Li RongQing <lirongqing@...du.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] net-sysfs: Ensure begin/complete are called in
 speed_show() and duplex_show()

On Wed, Feb 05, 2020 at 11:06:38AM +0200, Andy Shevchenko wrote:
> On Wed, Feb 05, 2020 at 04:16:16PM +0800, Kai-Heng Feng wrote:
> > Device like igb gets runtime suspended when there's no link partner. We
> > can't get correct speed under that state:
> > $ cat /sys/class/net/enp3s0/speed
> > 1000
> > 
> > In addition to that, an error can also be spotted in dmesg:
> > [  385.991957] igb 0000:03:00.0 enp3s0: PCIe link lost
> > 
> > It's because the igb device doesn't get runtime resumed before calling
> > get_link_ksettings().
> > 
> > So let's use a new helper to call begin() and complete() like what
> > dev_ethtool() does, to runtime resume/suspend or power up/down the
> > device properly.
> > 
> > Once this fix is in place, igb can show the speed correctly without link
> > partner:
> > $ cat /sys/class/net/enp3s0/speed
> > -1
> 
> What is the meaning of -1? Does it tells us "Hey, something is bad in hardware
> I can't tell you the speed" or does it imply anything else?

It's SPEED_UNKNOWN constant printed with "%d" template.

> Wouldn't be better to report 0?
> 
> Where is the documentation part of this ABI change?

It's not an ABI change, /sys/class/net/*/speed already shows -1 when the
device reports SPEED_UNKNOWN. The only change is that after this patch,
igb driver reports SPEED_UNKNOWN rather than an outdated value if there
is no link.

Michal