netdev - Re: [RFC PATCH 2/3] net: sparx5: Add Sparx5 switchdev driver

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Date:   Sun, 29 Nov 2020 10:52:45 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Steen Hegelund <steen.hegelund@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Microsemi List <microsemi@...ts.bootlin.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/3] net: sparx5: Add Sparx5 switchdev driver

On Sat, Nov 28, 2020 at 10:28:28PM +0000, Russell King - ARM Linux admin wrote:
> On Sat, Nov 28, 2020 at 08:06:16PM +0100, Andrew Lunn wrote:
> > > +static void sparx5_phylink_mac_config(struct phylink_config *config,
> > > +				      unsigned int mode,
> > > +				      const struct phylink_link_state *state)
> > > +{
> > > +	struct sparx5_port *port = netdev_priv(to_net_dev(config->dev));
> > > +	struct sparx5_port_config conf;
> > > +	int err = 0;
> > > +
> > > +	conf = port->conf;
> > > +	conf.autoneg = state->an_enabled;
> > > +	conf.pause = state->pause;
> > > +	conf.duplex = state->duplex;
> > > +	conf.power_down = false;
> > > +	conf.portmode = state->interface;
> > > +
> > > +	if (state->speed == SPEED_UNKNOWN) {
> > > +		/* When a SFP is plugged in we use capabilities to
> > > +		 * default to the highest supported speed
> > > +		 */
> > 
> > This looks suspicious.
> 
> Yes, it looks highly suspicious. The fact that
> sparx5_phylink_mac_link_up() is empty, and sparx5_phylink_mac_config()
> does all the work suggests that this was developed before the phylink
> re-organisation, and this code hasn't been updated for it.
> 
> Any new code for the kernel really ought to be updated for the new
> phylink methodology before it is accepted.
> 
> Looking at sparx5_port_config(), it also seems to use
> PHY_INTERFACE_MODE_1000BASEX for both 1000BASE-X and 2500BASE-X. All
> very well for the driver to do that internally, but it's confusing
> when it comes to reviewing this stuff, especially when people outside
> of the driver (such as myself) reviewing it need to understand what's
> going on with the configuration.

There are other issues too.

Looking at sparx5_get_1000basex_status(), we have:

 +       status->link = DEV2G5_PCS1G_LINK_STATUS_LINK_STATUS_GET(value) |
 +                      DEV2G5_PCS1G_LINK_STATUS_SYNC_STATUS_GET(value);

Why is the link status the logical OR of these?

 +                       if ((lp_abil >> 8) & 1) /* symmetric pause */
 +                               status->pause = MLO_PAUSE_RX | MLO_PAUSE_TX;
 +                       if (lp_abil & (1 << 7)) /* asymmetric pause */
 +                               status->pause |= MLO_PAUSE_RX;

is actually wrong, and I see I need to improve the documentation for
mac_pcs_get_state(). The intention in the documentation was concerning
hardware that indicated the _resolved_ status of pause modes. It was
not intended that drivers resolve the pause modes themselves.

Even so, the above is still wrong; it takes no account of what is being
advertised at the local end. If one looks at the implementation in
phylink_decode_c37_word(), one will notice there is code to deal with
this.

I think we ought to make phylink_decode_c37_word() and
phylink_decode_sgmii_word() public functions, and then this driver can
use these helpers to decode the link partner advertisement to the
phylink state.

Does the driver need to provide an ethtool .get_link function? That
seems to bypass phylink. Why can't ethtool_op_get_link() be used?

I think if ethtool_op_get_link() is used, we then have just one caller
for sparx5_get_port_status(), which means "struct sparx5_port_status"
can be eliminated and the code cleaned up to use the phylink decoding
helpers.

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