netdev - Re: [PATCH net-next] net: sfp: add debugfs support

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Date:   Wed, 2 Dec 2020 08:59:13 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Ido Schimmel <idosch@...sch.org>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Edwin Peer <edwin.peer@...adcom.com>,
        Vasundhara Volam <vasundhara-v.volam@...adcom.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Shannon Nelson <snelson@...sando.io>
Subject: Re: [PATCH net-next] net: sfp: add debugfs support

On Wed, 2 Dec 2020 13:03:18 +0000 Russell King - ARM Linux admin wrote:
> Jakub,
> 
> What's your opinion on this patch? It seems to have stalled...

Sorry, I think I expected someone to do the obvious questioning..

> On Tue, Nov 24, 2020 at 12:46:40PM +0200, Ido Schimmel wrote:
> > On Tue, Nov 24, 2020 at 09:49:16AM +0000, Russell King - ARM Linux admin wrote:  
> > > On Tue, Nov 24, 2020 at 10:41:51AM +0200, Ido Schimmel wrote:  
> > > > On Tue, Nov 24, 2020 at 01:14:31AM +0100, Andrew Lunn wrote:  
> > > > > On Mon, Nov 23, 2020 at 10:06:16PM +0000, Russell King wrote:  
> > > > > > Add debugfs support to SFP so that the internal state of the SFP state
> > > > > > machines and hardware signal state can be viewed from userspace, rather
> > > > > > than having to compile a debug kernel to view state state transitions
> > > > > > in the kernel log.  The 'state' output looks like:
> > > > > > 
> > > > > > Module state: empty
> > > > > > Module probe attempts: 0 0
> > > > > > Device state: up
> > > > > > Main state: down
> > > > > > Fault recovery remaining retries: 5
> > > > > > PHY probe remaining retries: 12

Perfectly reasonable, no objections.

> > > > > > moddef0: 0
> > > > > > rx_los: 1
> > > > > > tx_fault: 1
> > > > > > tx_disable: 1

These, tho, are standard SFP signals, right? Maybe we should put them
in struct ethtool_link_ext_state_info? I remember that various "vendor
tools" report those, maybe it'd be nice to have a standard way of
exposing those signals tru ethtool APIs?

Opinions welcome (let me CC more NIC people)!

> > > > > > Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>  
> > > > > 
> > > > > Hi Russell
> > > > > 
> > > > > This looks useful. I always seem to end up recompiling the kernel,
> > > > > which as you said, this should avoid.  
> > > > 
> > > > FWIW, another option is to use drgn [1]. Especially when the state is
> > > > queried from the kernel and not hardware. We are using that in mlxsw
> > > > [2][3].  
> > > 
> > > Presumably that requires /proc/kcore support, which 32-bit ARM doesn't
> > > have.  
> > 
> > Yes, it does seem to be required for live debugging. I mostly work with
> > x86 systems, I guess it's completely different for Andrew and you.