netdev - Re: [RFC PATCH] net: mvpp2: fix detection of 10G SFP modules

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Message-ID: <20181204101954.mphe2eezdie75bgd@sapphire.tkos.co.il>
Date:   Tue, 4 Dec 2018 12:19:54 +0200
From:   Baruch Siach <baruch@...s.co.il>
To:     Russell King <linux@...linux.org.uk>,
        Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [RFC PATCH] net: mvpp2: fix detection of 10G SFP modules

Hi Russell,

On Thu, Nov 29, 2018 at 10:00:43PM +0000, Russell King - ARM Linux wrote:
> On Thu, Nov 29, 2018 at 11:31:23AM -0800, Florian Fainelli wrote:
> > On 11/29/2018 4:49 AM, Baruch Siach wrote:
> > > The mvpp2_phylink_validate() relies on the interface field of
> > > phylink_link_state to determine valid link modes. However, when called
> > > from phylink_sfp_module_insert() this field in not initialized. The
> > > default switch case then excludes 10G link modes. This allows 10G SFP
> > > modules that are detected correctly to be configured at max rate of
> > > 2.5G.
> > > 
> > > Catch the uninitialized PHY mode case, and allow 10G rates.
> > > 
> > > Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>
> > > Cc: Antoine Tenart <antoine.tenart@...tlin.com>
> > > Signed-off-by: Baruch Siach <baruch@...s.co.il>
> > > ---
> > > Is that the right fix?
> > 
> > It would be a bit surprising that this is the right fix, you would
> > expect validate to be called once everything has been parsed
> > successfully from the SFP, is not that the case here? If not, can you
> > find out what happens?
> 
> Two calls are made - the first with PHY_INTERFACE_MODE_NA to
> determine what the advertising link mode may be, and then again
> once the interface mode has been selected from the advertising mask.
> 
> Why?
> 
> Consider a 4.3Mbps fiberchannel SFP plugged into a 1G-only MAC.
> If we did it as a single pass, we would end up passing an
> interface mode of 2500BASEX first time around which is illogical.

So you consider this to be the right fix, right?

I should have added:

Fixes: d97c9f4ab000b ("net: mvpp2: 1000baseX support")

Antoine, is this fix OK with you?

baruch

-- 
     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
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