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

[Russell King - ARM Linux <linux@armlinux.org.uk>]

On Tue, Dec 04, 2018 at 12:19:54PM +0200, Baruch Siach wrote:
> 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@bootlin.com>
> > > > Cc: Antoine Tenart <antoine.tenart@bootlin.com>
> > > > Signed-off-by: Baruch Siach <baruch@tkos.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.

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