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

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Message-Id: <20180709.182902.1637265651643155858.kimoto@cybertrust.co.jp>
Date:   Mon, 09 Jul 2018 18:29:02 +0900 (JST)
From:   Masahiko KIMOTO <masahiko.kimoto@...ertrust.co.jp>
To:     f.fainelli@...il.com
Cc:     fugang.duan@....com, andrew@...n.ch, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, hiraku.toyooka@...ertrust.co.jp
Subject: Re: [RFC PATCH 0/1] net: phy: skip autoneg of ethernet(fec) on
 network boot

Hello Florian,

  > 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 for your support.

Concening the problem about PAUSE/Asym_PAUSE advertisement you pointed out,
I could not understand your consideration.

Would you tell me more detail about it?


From: Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [RFC PATCH 0/1] net: phy: skip autoneg of ethernet(fec) on
 network boot
Date: Fri, 6 Jul 2018 11:41:23 -0700

  > 
  > 
  > 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
  > 

---------------------------------------------------------------------------
Masahiko KIMOTO,Ph.D. / Cybertrust Japan Co., Ltd. 
mail: masahiko.kimoto@...ertrust.co.jp
web: https://www.cybertrust.co.jp/ https://www.miraclelinux.com/