netdev - Re: [PATCH net-next] net: phy: consider latched link-down status in polling mode

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Message-Id: <20190208.220924.1009748238168528290.davem@davemloft.net>
Date:   Fri, 08 Feb 2019 22:09:24 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     hkallweit1@...il.com
Cc:     andrew@...n.ch, f.fainelli@...il.com, netdev@...r.kernel.org,
        linux@...linux.org.uk
Subject: Re: [PATCH net-next] net: phy: consider latched link-down status
 in polling mode

From: Heiner Kallweit <hkallweit1@...il.com>
Date: Wed, 6 Feb 2019 19:39:52 +0100

> The link status value latches link-down events. To get the current
> status we read the register twice in genphy_update_link(). There's
> a potential risk that we miss a link-down event in polling mode.
> This may cause issues if the user e.g. connects his machine to a
> different network.
> 
> On the other hand reading the latched value may cause issues in
> interrupt mode. Following scenario:
> 
> - After boot link goes up
> - phy_start() is called triggering an aneg restart, hence link goes
>   down and link-down info is latched.
> - After aneg has finished link goes up and triggers an interrupt.
>   Interrupt handler reads link status, means it reads the latched
>   "link is down" info. But there won't be another interrupt as long
>   as link stays up, therefore phylib will never recognize that link
>   is up.
> 
> Deal with both scenarios by reading the register twice in interrupt
> mode only.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>

Applied, thanks.