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

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Date:   Sun, 29 Nov 2020 11:28:14 +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 Sun, Nov 29, 2020 at 10:52:45AM +0000, Russell King - ARM Linux admin wrote:
> 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.

(Sorry, I keep spotting bits in the code - it's really not an easy
chunk of code to review.)

I'm also not sure that this is really correct:

+       status->serdes_link = !phy_validate(port->serdes, PHY_MODE_ETHERNET,
+                                           port->conf.portmode, NULL);

The documentation for phy_validate() says:

 * Used to check that the current set of parameters can be handled by
 * the phy. Implementations are free to tune the parameters passed as
 * arguments if needed by some implementation detail or
 * constraints. It will not change any actual configuration of the
 * PHY, so calling it as many times as deemed fit will have no side
 * effect.

and clearly, passing NULL for opts, gives the function no opportunity
to do what it's intended, so phy_validate() is being used for some
other purpose than that which the drivers/phy subsystem intends it to
be used for.

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