linux-kernel - Re: [PATCH net-next v4 3/6] net: lan966x: add port module support

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Message-ID: <YaC/OT0f2JKBPMOb@shell.armlinux.org.uk>
Date:   Fri, 26 Nov 2021 11:04:25 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc:     davem@...emloft.net, kuba@...nel.org, robh+dt@...nel.org,
        UNGLinuxDriver@...rochip.com, p.zabel@...gutronix.de,
        andrew@...n.ch, netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 3/6] net: lan966x: add port module support

On Fri, Nov 26, 2021 at 10:05:37AM +0100, Horatiu Vultur wrote:
> This patch adds support for netdev and phylink in the switch. The
> injection + extraction is register based. This will be replaced with DMA
> accees.
> 
> Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>

This looks mostly good now, thanks. There's one remaining issue:

> +int lan966x_port_pcs_set(struct lan966x_port *port,
> +			 struct lan966x_port_config *config)
> +{
> +	struct lan966x *lan966x = port->lan966x;
> +	bool inband_aneg = false;
> +	bool outband;
> +	int err;
> +
> +	lan966x_port_link_down(port);

This looks like something the MAC layer should be doing. Phylink won't
change the interface mode by just calling the PCS - it will do this
sequence, known as a major reconfiguration:

mac_link_down() (if the link was previously up)
mac_prepare()
mac_config()
if (pcs_config() > 0)
  pcs_an_restart()
mac_finish()

pcs_config() will also be called thusly:

if (pcs_config() > 0)
  pcs_an_restart()

to change the ethtool advertising mask which changes the inband advert
or the Autoneg bit, which has an effect only on your DEV_PCS1G_ANEG_CFG()
register, and this may be called with the link up or down.

Also, pcs_config() is supposed to return 0 if the inband advert has not
changed, or positive if it has (so pcs_an_restart() is called to cause
in-band negotiation to be restarted.)

Note also that pcs_an_restart() may  also be called when ethtool
requests negotiation restart when we're operating in 802.3z modes.

So, my question is - do you need to be so heavy weight with the call to
lan966x_port_link_down() to take everything down when pcs_config() is
called, and is it really in the right place through the sequence for
a major reconfiguration?

Thanks.

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