From: Vladimir Oltean <olteanv@gmail.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Marcin Wojtas <mw@semihalf.com>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
davem@davemloft.net, kuba@kernel.org, linux@armlinux.org.uk,
jaz@semihalf.com, gjb@semihalf.com, upstream@semihalf.com,
Samer.El-Haj-Mahmoud@arm.com, jon@solid-run.com, tn@semihalf.com,
rjw@rjwysocki.net, lenb@kernel.org
Subject: Re: [net-next: PATCH v3 1/6] Documentation: ACPI: DSD: describe additional MAC configuration
Date: Thu, 24 Jun 2021 00:42:18 +0300 [thread overview]
Message-ID: <20210623214218.eaq4uflmxnkbl4dw@skbuf> (raw)
In-Reply-To: <YNOW+mQNEmSRx/6V@lunn.ch>
Hi Andrew,
On Wed, Jun 23, 2021 at 10:18:02PM +0200, Andrew Lunn wrote:
> > +MAC node example with a "fixed-link" subnode.
> > +---------------------------------------------
> > +
> > +.. code-block:: none
> > +
> > + Scope(\_SB.PP21.ETH1)
> > + {
> > + Name (_DSD, Package () {
> > + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > + Package () {
> > + Package () {"phy-mode", "sgmii"},
> > + },
> > + ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
> > + Package () {
> > + Package () {"fixed-link", "LNK0"}
> > + }
> > + })
>
> At least in the DT world, it is pretty unusual to see both fixed-link
> and phy-mode. You might have one of the four RGMII modes, in order to
> set the delays when connecting to a switch. But sgmii and fixed link
> seems very unlikely, how is sgmii autoneg going to work?
SGMII autoneg is supposed to be disabled if you have a fixed-link, and
there is nothing unusual in that kind of setup.
There are 3 types of phylink setups:
MLO_AN_INBAND: there might or might not be a phy-handle, but SGMII
autoneg should be enabled and the MAC should be
reconfigured automatically (in hardware) to the right
speed/duplex based on that
MLO_AN_PHY: there is a phy-handle but SGMII autoneg should be disabled*
and the MAC should be reconfigured (forced) in software to
the speed/duplex determined by reading the PHY MDIO
registers
MLO_AN_FIXED: there is no phy-handle or phy_device, but the driver
should do the same thing, the speed/duplex is configured
by management (in this case DT/ACPI)
*there appears to be some debate here, since the "managed" property is
phylink-specific and therefore a phylib driver will not necessarily
disable its in-band autoneg, but this is what the existing phylink_pcs
drivers in drivers/net/pcs/ do and I think there's nothing wrong with
settling on that if phylink is being used. It does create some interesting
questions though when a driver is being converted from phylib to phylink,
since the meaning of the existing firmware bindings suddenly changes.
An SGMII link with MLO_AN_FIXED is nothing unusual, it is in fact very
widespread as a way to reduce pin count compared to the parallel RGMII.
I suspect there are more DSA setups in the field with an SGMII fixed-link
than with RGMII fixed-link, due to practicality.
The 2 characteristic features of SGMII compared to 1000base-X are:
- customization of the 16-bit configuration word communicated via the
clause 37 state machines. Those are bypassed in MLO_AN_PHY and
MLO_AN_FIXED modes, true
- symbol replication at 10/100 speeds.
So since it is equally valid to have an SGMII fixed-link at 100Mbps or
10Mbps, it is just as valid to have an SGMII fixed-link at 1Gbps with
in-band autoneg disabled.
next prev parent reply other threads:[~2021-06-23 21:42 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-21 17:30 [net-next: PATCH v3 0/6] ACPI MDIO support for Marvell controllers Marcin Wojtas
2021-06-21 17:30 ` [net-next: PATCH v3 1/6] Documentation: ACPI: DSD: describe additional MAC configuration Marcin Wojtas
2021-06-23 20:18 ` Andrew Lunn
2021-06-23 21:00 ` Marcin Wojtas
2021-06-23 21:36 ` Andrew Lunn
2021-06-23 21:42 ` Vladimir Oltean [this message]
2021-06-21 17:30 ` [net-next: PATCH v3 2/6] net: mdiobus: Introduce fwnode_mdbiobus_register() Marcin Wojtas
2021-06-23 20:22 ` Andrew Lunn
2021-06-23 22:10 ` Marcin Wojtas
2021-06-24 11:10 ` Marcin Wojtas
2021-06-21 17:30 ` [net-next: PATCH v3 3/6] net/fsl: switch to fwnode_mdiobus_register Marcin Wojtas
2021-06-23 20:24 ` Andrew Lunn
2021-06-21 17:30 ` [net-next: PATCH v3 4/6] net: mvmdio: add ACPI support Marcin Wojtas
2021-06-23 20:28 ` Andrew Lunn
2021-06-23 21:58 ` Marcin Wojtas
2021-06-24 1:24 ` Andrew Lunn
2021-06-21 17:30 ` [net-next: PATCH v3 5/6] net: mvpp2: enable using phylink with ACPI Marcin Wojtas
2021-06-23 20:37 ` Andrew Lunn
2021-06-23 21:45 ` Marcin Wojtas
2021-06-24 1:17 ` Andrew Lunn
2021-06-21 17:30 ` [net-next: PATCH v3 6/6] net: mvpp2: remove unused 'has_phy' field Marcin Wojtas
2021-06-23 11:56 ` [net-next: PATCH v3 0/6] ACPI MDIO support for Marvell controllers Marcin Wojtas
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