linux-kernel - Re: [RFC PATCH 0/1] net: phy: skip autoneg of ethernet(fec) on network boot

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Message-ID: <8a437ead-5ded-57c4-c44f-95986442d626@gmail.com>
Date:   Fri, 6 Jul 2018 11:41:23 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Masahiko Kimoto <masahiko.kimoto@...ertrust.co.jp>,
        Fugang Duan <fugang.duan@....com>,
        Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hiraku Toyooka <hiraku.toyooka@...ertrust.co.jp>
Subject: Re: [RFC PATCH 0/1] net: phy: skip autoneg of ethernet(fec) on
 network boot



On 07/05/2018 11:07 PM, Masahiko Kimoto wrote:
> Hello,
> 
> This patch introduces auto negotiation skipping for Ethernet.
> It is useful to shorten boot time on network boot like the following
> environment;
> 
>  - target board is NXP i.MX6.
>  - NIC is fec.
>  - using u-boot as boot loader.
>  - boot from kernel and initramfs obtained via TFTP.
>  - mount remote file system and switch root to that.
>  - thus all file system is on network.
> 
> In this case, u-boot and kernel initialize NIC three times,
> once in boot loader, once in device attach and once more in phy attach.
> Each causes link auto negotiation and wait several seconds.
> However link state is stable after reset by boot loader, therefore we
> can skip hardware re-initialization of NIC in kernel.
> 
> The patch skips link down in Ethernet(i.MX's fec) driver and initialization
> in PHY layer if kernel option 'anegskip' is supplied.
> 
> By this patch boot time becomes 3secs shorter.
> 
> I think current patch is dirty hack, because;
>  - modification is split into PHY and Ethernet driver.
>  - in the case of two or more Ethernet I/F exist, currently there is
>    no way to specify whith I/F skips autonego.
> 
> I would like to implement such skpping auto negotiation feature in generic
> framework. How should we implement these requirements?

I completely acknowledge and support the use case, but your
implementation is definitively not the way to go. In my experience the
problem is usually that there may be a disagreement on the
Pause/Asym_Pause advertisement bits and that alone is responsible for
triggering a re-negotiation. Can yo check if that is the case here?

Thank you
-- 
Florian