netdev - Re: [PATCH] net: phy: micrel: Fix detection of ksz87xx switch

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Message-ID: <20210807000123.GA4898@cephalopod>
Date:   Sat, 7 Aug 2021 02:01:24 +0200
From:   Ben Hutchings <ben.hutchings@...ensium.com>
To:     Steve Bennett <steveb@...kware.net.au>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: micrel: Fix detection of ksz87xx switch

On Sat, Jul 31, 2021 at 08:19:17AM +1000, Steve Bennett wrote:
> > On 31 Jul 2021, at 2:59 am, Jakub Kicinski <kuba@...nel.org> wrote:
> > 
> > Please extend the CC list to the maintainers, and people who
> > worked on this driver in the past, especially Marek.
> 
> Sure, I can do that in a v2 of the patch along with the more detailed
> explanation below.
> 
> > 
> > On Fri, 30 Jul 2021 20:51:20 +1000 Steve Bennett wrote:
> >> The previous logic was wrong such that the ksz87xx
> >> switch was not identified correctly.
> > 
> > Any more details of what is happening? Which extact device do you see
> > this problem on?
> 
> I have a ksz8795 switch.
> 
> Without the patch:
> 
> ksz8795-switch spi3.1 ade1 (uninitialized): PHY [dsa-0.1:03] driver [Generic PHY]
> ksz8795-switch spi3.1 ade2 (uninitialized): PHY [dsa-0.1:04] driver [Generic PHY]
> 
> With the patch:
> 
> ksz8795-switch spi3.1 ade1 (uninitialized): PHY [dsa-0.1:03] driver [Micrel KSZ87XX Switch]
> ksz8795-switch spi3.1 ade2 (uninitialized): PHY [dsa-0.1:04] driver [Micrel KSZ87XX Switch]
[...]

And do the external ports work for you after this?

I have a development board with a KSZ8795.  All ports worked before
this patch.  After this patch, when I bring up the external ports they
are reported as having link up at 10M half duplex, when the link is
actually down.

The ksz8873mll_read_status() function is trying to read a non-standard
MDIO register that is not handled by the ksz8795 driver's MDIO
emulation (and is not documented as existing on the KSZ8873MLL,
either!).  It also also reports link up, which is obviously not
correct for an external port.

I'll post a patch as a reply to this.

Ben.

-- 
Ben Hutchings · Senior Embedded Software Engineer, Essensium-Mind · mind.be