netdev - Re: [PATCH RFC net-next 1/5] net: dsa: mt7530: Convert to PHYLINK API

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Message-ID: <CA+h21hqK0VMtHpZ6eka9ESuMhsFTw2mx+c0GYmxq4_G_YmiVpg@mail.gmail.com>
Date:   Wed, 26 Jun 2019 01:14:59 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     René van Dorst <opensource@...rst.com>,
        sean.wang@...iatek.com, Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, matthias.bgg@...il.com,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        frank-w@...lic-files.de, netdev <netdev@...r.kernel.org>,
        linux-mediatek@...ts.infradead.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH RFC net-next 1/5] net: dsa: mt7530: Convert to PHYLINK API

On Wed, 26 Jun 2019 at 00:53, Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Tue, Jun 25, 2019 at 11:24:01PM +0300, Vladimir Oltean wrote:
> > Hi Russell,
> >
> > On 6/24/19 6:39 PM, Russell King - ARM Linux admin wrote:
> > > This should be removed - state->link is not for use in mac_config.
> > > Even in fixed mode, the link can be brought up/down by means of a
> > > gpio, and this should be dealt with via the mac_link_* functions.
> > >
> >
> > What do you mean exactly that state->link is not for use, is that true in
> > general?
>
> Yes.  mac_config() should not touch it; it is not always in a defined
> state.  For example, if you set modes via ethtool (the
> ethtool_ksettings_set API) then state->link will probably contain
> zero irrespective of the true link state.
>

Experimentally, state->link is zero at the same time as state->speed
is -1, so just ignoring !state->link made sense. This is not in-band
AN. What is your suggestion? Should I proceed to try and configure the
MAC for SPEED_UNKNOWN?

> It exists in this structure because it was convenient to just use one
> structure to store all the link information in various parts of the
> code, and when requesting the negotiated in-band MAC configuration.
>
> I've come to the conclusion that that decision was a mistake, based
> on patches such as the above mistakenly thinking that everything in
> the state structure is fair game.  I've since updated the docs to
> explicitly spell it out, but I'm also looking at the feasibility of
> changing the mac_config() interface entirely - splitting it into two
> (mac_config_fixed() and mac_config_inband()) and passing only the
> appropriate parameters to each.
>
> However, having looked at that, I think such a change will make some
> MAC drivers quite a bit more complicated - having all the config
> steps in one method appears to make the configuration of MAC drivers
> easier (eg, mvneta, mvpp2.)
>
> > In drivers/net/dsa/sja1105/sja1105_main.c, if I remove the "if
> > (!state->link)" guard, I see PHYLINK calls with a SPEED_UNKNOWN argument for
> > ports that are BR_STATE_DISABLED. Is that normal?
>
> This looks like another driver which has been converted to phylink
> without my review; I certainly wasn't aware of it.  It gets a few
> things wrong, such as:
>
> 1) not checking state->interface in the validate callback - so it
>    is basically saying that it can support any PHY interface mode
>    that the kernel happens to support.
>

Partially true. It does check the DT bindings for supported MII modes
in sja1105_init_mii_settings (for fundamental reasons... the switch
expects an 'all-in-one' configuration buffer with the operating modes
of all MACs - don't ask me to delay the uploading of this static
config until all ports collected their interface_mode from phylink via
the mac_config callback - it's a deadlock).
It is a gigabit switch with MII/RMII/RGMII MACs - I have never seen
any PHY wired for these modes that can change system interface type.

> 2) if phylink is configured to use in-band, then state->speed is
>    undefined; this driver will fail.  (If folk don't want to support
>    that, we ought to have a way to tell phylink to reject anything
>    that attempts to set it to in-band mode!)
>

Ok.

> 3) it doesn't implement phylink_mac_link_state DSA ops, so it doesn't
>    support SGMII or 802.3z phy interface modes (see 1).
>

No, it doesn't.
Some odd switch in this device family supports SGMII on 1 of its
ports, however I haven't put my hands on it.
When I do I'll add checks for strange scenarios, like connecting it to
an Aquantia PHY that can switch between SGMII and USXGMII (although
why would anyone pair a 10G capable PHY to a 1G capable MAC...)

> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
> According to speedtest.net: 11.9Mbps down 500kbps up

Thanks,
-Vladimir