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

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Date:   Tue, 4 Dec 2018 13:31:54 +0200
From:   Baruch Siach <baruch@...s.co.il>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Antoine Tenart <antoine.tenart@...tlin.com>,
        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 Tue, Dec 04, 2018 at 10:27:01AM +0000, Russell King - ARM Linux wrote:
> On Tue, Dec 04, 2018 at 12:19:54PM +0200, Baruch Siach wrote:
> > 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?
> 
> Yes, but there is another bug lurking here - the handling of invalid
> interface modes is not correct.  Please see mvneta.c as an example -
> interface modes that are not supported by the MAC (apart from the NA
> mode) end up with the supported mask completely cleared.

I'll take this as an ack. Thanks for reviewing.

I plan to resend this patch with your ack and a proper Fixes tag. I'll then 
add another patch to properly handle the invalid mode case.

Thanks,
baruch

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