netdev - Re: [PATCH net-next v2 1/8] net: phylink: propagate resolved link config via mac_link

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Date:   Wed, 26 Feb 2020 19:11:51 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Ioana Ciornei <ioana.ciornei@....com>
Cc:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        Jonathan Corbet <corbet@....net>,
        Michal Simek <michal.simek@...inx.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        John Crispin <john@...ozen.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        netdev <netdev@...r.kernel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Felix Fietkau <nbd@....name>
Subject: Re: [PATCH net-next v2 1/8] net: phylink: propagate resolved link
 config via mac_link_up()

On Wed, Feb 26, 2020 at 06:32:55PM +0000, Ioana Ciornei wrote:
> > Subject: Re: [PATCH net-next v2 1/8] net: phylink: propagate resolved link config
> > via mac_link_up()
> > 
> > On Wed, 26 Feb 2020 at 20:21, Vladimir Oltean <olteanv@...il.com> wrote:
> > >
> > > On Wed, 26 Feb 2020 at 15:36, Russell King - ARM Linux admin
> > > <linux@...linux.org.uk> wrote:
> > > >
> > > >
> > > > dpaa2 is complicated by the firmware, and that we can't switch the
> > > > interface mode between (SGMII,1000base-X) and 10G.
> > > >
> > > > If the firmware is in "DPMAC_LINK_TYPE_PHY" mode, it expects to be
> > > > told the current link parameters via the dpmac_set_link_state() call
> > > > - it isn't clear whether that needs to be called for other modes
> > > > with the up/down state (firmware API documentation is poor.)
> > > >
> > >
> > > With PCS control in Linux, I am pretty sure that you don't want
> > > anything other than DPMAC_LINK_TYPE_PHY anyway.
> > > Basically in DPMAC_LINK_TYPE_FIXED, the MC firmware is in control of
> > > the PCS and polls its link state to emit link notifications to objects
> > > connected to the DPMAC. So Linux control of PCS would class with
> > 
> > s/class/clash/
> > 
> > > firmware control of the PCS, leading to undesirable side-effects to
> > > say the least.
> 
> 
> If the DPMAC object is in DPMAC_LINK_TYPE_FIXED, the dpaa2-eth in fact
> does not even connect to a phy so all the phylink interaction is not happening.
> As Vladimir said, in this case it's the MC firmware's job to poll the PCS and
> notify any connected objects of a link change.

Please see the patches I've referred Vladimir to, specifically this:

        if (attr.link_type == DPMAC_LINK_TYPE_PHY) {
                /* FIXME: how do we know whether this DPMAC has a PCS? */
                err = dpaa2_pcs_create(mac, attr.id);
                if (err)
                        goto err_phylink_destroy;

                phylink_add_pcs(mac->phylink, &dpaa2_pcs_phylink_ops);
        }

Hence, if we are not in DPMAC_LINK_TYPE_PHY, then we never talk to
the PCS, thereby satisfying the requirements of the firmware not to
touch the PCS if it's in FIXED mode.

It seems this is becoming a storm in a tea cup.  Please stop.

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