linux-kernel - Re: [PATCH 07/14] net: axienet: Fix SGMII support

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Message-ID: <20200110150409.GD25745@shell.armlinux.org.uk>
Date:   Fri, 10 Jan 2020 15:04:09 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        Michal Simek <michal.simek@...inx.com>,
        Robert Hancock <hancock@...systems.ca>, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/14] net: axienet: Fix SGMII support

On Fri, Jan 10, 2020 at 02:20:38PM +0000, Andre Przywara wrote:
> On Fri, 10 Jan 2020 15:04:15 +0100
> Andrew Lunn <andrew@...n.ch> wrote:
> 
> Hi Andrew,
> 
> > On Fri, Jan 10, 2020 at 11:54:08AM +0000, Andre Przywara wrote:
> > > With SGMII, the MAC and the PHY can negotiate the link speed between
> > > themselves, without the host needing to mediate between them.
> > > Linux recognises this, and will call phylink's mac_config with the speed
> > > member set to SPEED_UNKNOWN (-1).
> > > Currently the axienet driver will bail out and complain about an
> > > unsupported link speed.
> > > 
> > > Teach axienet's mac_config callback to leave the MAC's speed setting
> > > alone if the requested speed is SPEED_UNKNOWN.  
> > 
> > Hi Andre
> > 
> > Is there an interrupt when SGMII signals a change in link state? If
> > so, you should call phylink_mac_change().
> 
> Good point. The doc describes a "Auto-Negotiation Complete" interrupt
> status bit, which signal that " ... auto-negotiation of the SGMII or
> 1000BASE-X interface has completed."

It depends what they mean by "Auto-negotiation complete" in SGMII.
SGMII can complete the handshake, yet the config_reg word indicate
link down.  If such an update causes an "Auto-negotiation complete"
interrupt, then that's sufficient.

However, looking at axienet_mac_pcs_get_state(), that is just reading
back what the MAC was set to in axienet_mac_config(), which is not
how this is supposed to work.  axienet_mac_pcs_get_state() is
supposed to get the results of the SGMII/1000BASE-X "negotiation".
That also needs to be fixed.

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