linux-kernel - Re: [EXT] Re: [PATCH net-next 5/6] arm64: dts: marvell: mcbin: enable the fourth network interface

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Date:   Wed, 3 Jan 2018 19:17:14 +0100
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Stefan Chulski <stefanc@...vell.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Yan Markman <ymarkman@...vell.com>,
        Jason Cooper <jason@...edaemon.net>,
        netdev <netdev@...r.kernel.org>,
        Antoine Tenart <antoine.tenart@...e-electrons.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kishon@...com" <kishon@...com>, Nadav Haklai <nadavh@...vell.com>,
        Miquèl Raynal <miquel.raynal@...e-electrons.com>,
        Gregory Clément 
        <gregory.clement@...e-electrons.com>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [EXT] Re: [PATCH net-next 5/6] arm64: dts: marvell: mcbin: enable
 the fourth network interface

Russell,

2018-01-03 18:54 GMT+01:00 Russell King - ARM Linux <linux@...linux.org.uk>:
> On Wed, Jan 03, 2018 at 05:00:47PM +0000, Stefan Chulski wrote:
>> > > > -----Original Message-----
>> > > > Hi Russell,
>> > > >
>> > > > Indeed. RGMII MAC behaves same way, although it shouldn't be named
>> > > > as 'in- band' to be on par with the specifications. Anyway - this
>> > > > one is rather a stub for being able to work with ACPI, so once the
>> > > > MDIO bus works there, this will be out of any concerns.
>> > >
>> > > Hi Marcin,
>> > >
>> > > This is correct.
>> > > "in-band" supported only for SGMII mode.
>> > > IRQ link interrupt depend on "in-band"' auto negation only if "in-band"'
>> > enabled.
>> > > But IRQ link interrupt could be triggered with "in-band", "out-band" or with
>> > specific fixed speed/duplex/flow_contol.
>> >
>> > Hi Stefan,
>> >
>> > How does this work in RGMII mode - is this handled by the PP2 polling the PHY
>> > to get the speed, duplex and flow control settings?
>> >
>>
>> IRQ interrupt doesn't handled speed, duplex and flow control settings.
>> It's just raised if number of criterions met:
>> 1) Physical signal detected by MAC
>> 2) MAC auto negotiation succeeded(valid only auto negotiation enabled in MAC and "in-band" bypass disabled)
>>
>> So if auto negotiation mechanism disabled in MAC or bypassed, link status would changes to up and IRQ interrupt be triggered.
>>
>> In case of RGMII mode obviously we don't have "in-band" auto negotiation and "out-band" cannot be used in Kernel(due to missed locks).
>> So auto negotiation should be disabled on MAC level and speed/duplex/flow_contol would be negotiate by PHY.
>> phylink/phylib infrastructure should provide speed/duplex/flow_contol(that were agreed between PHY's) to ppv2 driver.
>
> Sorry, I find this very confusing.
>
> It seems we have some people telling me that when there's no PHY
> described in DT, we use this link interrupt, and have a functional
> network interface (presumably at whatever speed.)
>
> I can't see this working from what you describe - what you describe
> basically tells me that when in-band autonegotiation is disabled, and we
> have no PHY in the kernel, then effectively we are in fixed-link mode -
> since we need to know what speed, duplex and flow control settings to
> use.
>
> So, this means that mvpp2 should be enforcing the presence of a
> fixed-link description in DT if there is no PHY node at the moment, but
> it doesn't.
>
> Instead, it looks to me like the speed and duplex settings are inherited
> from the boot loader or whatever was running before - I can't find
> anything that configures MVPP2_GMAC_AUTONEG_CONFIG in this case.  That
> seems quite a mess.

Just 3 cents from me about the RGMII + link IRQ, which is only a
temporary solution for ACPI. It works basing on the results of UEFI HW
PHY polling and inherited GMAC settings. Once this MDIO bus / PHY
handling lands, this configuration will be out of any question and
usage in the pp2 driver.

Marcin

>
> Maybe I'm missing something, but I don't see how mvpp2 can be converted
> to phylink given this without causing some kind of regression, unless
> someone can be much clearer about exactly what kinds of link mvpp2
> supports and how they work (which is basically what I asked back in
> October.)
>
> --
> RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up
> According to speedtest.net: 8.21Mbps down 510kbps up