linux-kernel - Re: [PATCH net-next 1/2] net: phy: marvell-88x2222: check that link is operational

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Message-ID: <20210413071930.52vfjkewkufl7hrb@dhcp-179.ddg>
Date:   Tue, 13 Apr 2021 10:19:30 +0300
From:   Ivan Bornyakov <i.bornyakov@...rotek.ru>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     system@...rotek.ru, hkallweit1@...il.com, linux@...linux.org.uk,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] net: phy: marvell-88x2222: check that link
 is operational

On Tue, Apr 13, 2021 at 01:40:32AM +0200, Andrew Lunn wrote:
> On Mon, Apr 12, 2021 at 03:16:59PM +0300, Ivan Bornyakov wrote:
> > Some SFP modules uses RX_LOS for link indication. In such cases link
> > will be always up, even without cable connected. RX_LOS changes will
> > trigger link_up()/link_down() upstream operations. Thus, check that SFP
> > link is operational before actual read link status.
> 
> Sorry, but this is not making much sense to me.
> 
> LOS just indicates some sort of light is coming into the device. You
> have no idea what sort of light. The transceiver might be able to
> decode that light and get sync, it might not. It is important that
> mv2222_read_status() returns the line side status. Has it been able to
> achieve sync? That should be independent of LOS. Or are you saying the
> transceiver is reporting sync, despite no light coming in?
> 
> 	Andrew

Yes, with some SFP modules transceiver is reporting sync despite no
light coming in. So, the idea is to check that link is somewhat
operational before determing line-side status.