netdev - Re: [PATCH] net: sfp: workaround GPIO input signals bounce

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Date:   Tue, 13 Sep 2022 12:54:26 +0300
From:   Baruch Siach <baruch@...s.co.il>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Baruch Siach <baruch.siach@...lu.com>
Subject: Re: [PATCH] net: sfp: workaround GPIO input signals bounce

Hi Russell,

On Tue, Sep 13 2022, Russell King (Oracle) wrote:
> On Tue, Sep 13, 2022 at 10:43:38AM +0300, Baruch Siach wrote:
>> From: Baruch Siach <baruch.siach@...lu.com>
>> 
>> Add a trivial debounce to avoid miss of state changes when there is no
>> proper hardware debounce on the input signals. Otherwise a GPIO might
>> randomly indicate high level when the signal is actually going down,
>> and vice versa.
>> 
>> This fixes observed miss of link up event when LOS signal goes down on
>> Armada 8040 based system with an optical SFP module.
>
> NAK. This needs more inteligent handling. For systems where we poll,
> your code introduces a 100us delay each time we poll and there has
> been no change.

I think we can avoid delay in the poll case by skipping the delay loop
when sfp->need_poll is true.

I'll send v2 with that fixed tomorrow.

Thanks for reviewing,
baruch

-- 
                                                     ~. .~   Tk Open Systems
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