linux-kernel - Re: [PATCH] net: sfp: reset fault retry counter on successful reinitialisation

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Date:   Fri, 12 Aug 2022 17:45:26 +0200
From:   Stefan Mahr <dac922@....de>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sfp: reset fault retry counter on successful
 reinitialisation

> On Fri, Aug 12, 2022 at 03:04:38PM +0200, Stefan Mahr wrote:
>> This patch resets the fault retry counter to the default value, if the
>> module reinitialisation was successful. Otherwise without resetting
>> the counter, five (N_FAULT/N_FAULT_INIT) single TX_FAULT events will
>> deactivate the module persistently.
>
> This is intentional - if a module keeps asserting its TX_FAULT status,
> then there is something wrong with it, and for an optical module it
> means that the laser is overloading (producing more output than it
> should.) That is a safety issue.

Yes, this behaviour is not changed by the patch. When TX_FAULT is true
persistently for 5 retries, the module will still be disabled.

>
> So, if the module keeps indicating that its laser is misbehaving the
> only right thing to do is to shut it down permanently, and have
> someone investigate.
>
> What issue are you seeing that needs a different behaviour?
>

In my case two different SFP modules (1000Base-BX) indicate short
TX_FAULT events for less than one second and only one per week -
sometimes more, sometimes less. So the idea was to reset the counter if
reinitialisation was successful, so rare single TX_FAULT events can be
ignored.

However, you are right: If a module reports TX_FAULT several times,
something serious may be wrong.