netdev - Re: [PATCH v3 1/3] net: dsa: mv88e6xxx: Don't force link when using in-band-status

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Date:   Tue, 20 Oct 2020 22:18:14 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     Marek Behun <marek.behun@....cz>, Andrew Lunn <andrew@...n.ch>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "olteanv@...il.com" <olteanv@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] net: dsa: mv88e6xxx: Don't force link when using
 in-band-status

On Tue, Oct 20, 2020 at 09:06:32PM +0000, Chris Packham wrote:
> 
> On 21/10/20 3:51 am, Marek Behun wrote:
> > On Tue, 20 Oct 2020 15:15:25 +0100
> > Russell King - ARM Linux admin <linux@...linux.org.uk> wrote:
> >
> >> On Tue, Oct 20, 2020 at 04:05:35PM +0200, Andrew Lunn wrote:
> >>> On Tue, Oct 20, 2020 at 03:49:40PM +0200, Marek Behun wrote:
> >>>> On Tue, 20 Oct 2020 11:15:52 +0100
> >>>> Russell King - ARM Linux admin <linux@...linux.org.uk> wrote:
> >>>>    
> >>>>> On Tue, Oct 20, 2020 at 04:45:56PM +1300, Chris Packham wrote:
> >>>>>> When a port is configured with 'managed = "in-band-status"' don't force
> >>>>>> the link up, the switch MAC will detect the link status correctly.
> >>>>>>
> >>>>>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> >>>>>> Reviewed-by: Andrew Lunn <andrew@...n.ch>
> >>>>> I thought we had issues with the 88E6390 where the PCS does not
> >>>>> update the MAC with its results. Isn't this going to break the
> >>>>> 6390? Andrew?
> >>>>>    
> >>>> Russell, I tested this patch on Turris MOX with 6390 on port 9 (cpu
> >>>> port) which is configured in devicetree as 2500base-x, in-band-status,
> >>>> and it works...
> >>>>
> >>>> Or will this break on user ports?
> >>> User ports is what needs testing, ideally with an SFP.
> >>>
> >>> There used to be explicit code which when the SERDES reported link up,
> >>> the MAC was configured in software with the correct speed etc. With
> >>> the move to pcs APIs, it is less obvious how this works now, does it
> >>> still software configure the MAC, or do we have the right magic so
> >>> that the hardware updates itself.
> >> It's still there. The speed/duplex etc are read from the serdes PHY
> >> via mv88e6390_serdes_pcs_get_state(). When the link comes up, we
> >> pass the negotiated link parameters read from there to the link_up()
> >> functions. For ports where mv88e6xxx_port_ppu_updates() returns false
> >> (no external PHY) we update the port's speed and duplex setting and
> >> (currently, before this patch) force the link up.
> >>
> >> That was the behaviour before I converted the code, the one that you
> >> referred to. I had assumed the code was correct, and _none_ of the
> >> speed, duplex, nor link state was propagated from the serdes PCS to
> >> the port on the 88E6390 - hence why the code you refer to existed.
> >>
> > Russell, you are right.
> > SFP on 88E6390 does not work with this patch applied.
> > So this patch breaks 88E6390.
> Thanks for testing. It sounds like maybe if I make 
> mv88e6xxx_port_ppu_updates() return true for the 6097 in serdes mode I 
> can avoid the forced link up without affecting the 6390.

Another option would be to make mv88e6xxx_mac_link_up() call a
switch specific implementation function, which is probably way
cleaner than introducing conditionals on the switch type in
functions, and reflects the existing code structure.

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