netdev - Re: Phylink flow control support on ports with MLO_AN

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Message-ID: <20210131103549.GA1463@shell.armlinux.org.uk>
Date:   Sun, 31 Jan 2021 10:35:49 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Stefan Chulski <stefanc@...vell.com>
Cc:     "andrew@...n.ch" <andrew@...n.ch>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Marcin Wojtas (mw@...ihalf.com)" <mw@...ihalf.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Yan Markman <ymarkman@...vell.com>
Subject: Re: Phylink flow control support on ports with  MLO_AN_FIXED auto
 negotiation

On Sun, Jan 31, 2021 at 10:12:25AM +0000, Stefan Chulski wrote:
> Hi,
> 
> Armada has options for 1G/10G ports without PHY's(for example community board Macchiato single shot).
> This port doesn't have PHY's and cannot negotiate Flow Control support, but we can for example connect two ports without PHY's and manually(by ethtool) configure FC.

On the Macchiatobin single shot, you use the existing SFP support
rather than forcing them to fixed link.

> Current phylink return error if I do this on ports with MLO_AN_FIXED(callback phylink_ethtool_set_pauseparam):
> if (pl->cur_link_an_mode == MLO_AN_FIXED)
>                 return -EOPNOTSUPP;
> 
> How can we enable FC configurations for these ports? Do you have any suggestions or should I post my proposal as an RFC patch?

If you really must use fixed-link, you specify the pause modes via
firmware, just as you specify the speed and duplex - you specify
the link partner's flow control abilities.

-- 
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