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

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Message-ID: <20181129220043.GB30658@n2100.armlinux.org.uk>
Date:   Thu, 29 Nov 2018 22:00:43 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Baruch Siach <baruch@...s.co.il>, netdev@...r.kernel.org,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>
Subject: Re: [RFC PATCH] net: mvpp2: fix detection of 10G SFP modules

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.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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