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From: Sascha Hauer <s.hauer@pengutronix.de>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: netdev@vger.kernel.org, devicetree@vger.kernel.org,
	kernel@pengutronix.de, linux-kernel@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] net: ethernet: mvneta: add support for 2.5G DRSGMII mode
Date: Tue, 9 Jun 2020 14:11:31 +0200	[thread overview]
Message-ID: <20200609121131.GJ11869@pengutronix.de> (raw)
In-Reply-To: <20200608160801.GO1551@shell.armlinux.org.uk>

On Mon, Jun 08, 2020 at 05:08:01PM +0100, Russell King - ARM Linux admin wrote:
> On Mon, Jun 08, 2020 at 09:47:16AM +0200, Sascha Hauer wrote:
> > The Marvell MVNETA Ethernet controller supports a 2.5 Gbps SGMII mode
> > called DRSGMII.
> > 
> > This patch adds a corresponding phy-mode string 'drsgmii' and parses it
> > from DT. The MVNETA then configures the SERDES protocol value
> > accordingly.
> > 
> > It was successfully tested on a MV78460 connected to a FPGA.
> 
> Digging around, this is Armada XP?  Which SoCs is this mode supported?
> There's no mention of DRSGMII in the A38x nor A37xx documentation which
> are later than Armada XP.

It's an Armada XP MV78460 in my case. I have no idea what other SoCs
this mode is supported on.

> 
> What exactly is "drsgmii"?  It can't be "double-rate" SGMII because that
> would give you 2Gbps max instead of the 1Gbps, but this gives 2.5Gbps,
> so I'm really not sure using "drsgmii" is a good idea.  It may be what
> Marvell call it, but we really need to know if there's some vendor
> neutral way to refer to it.

The abbreviation really is for "Double Rated SGMII". It seems it has 2.5
times the clock rate than ordinary SGMII. Another term I found is HSGMII
(High serial gigabit media-independent interface) which also has
2.5Gbps.

Anyway, I just learned from the paragraph you added to
Documentation/networking/phy.rst that 1000BASEX differs from SGMII in
the format of the control word. As we have a fixed link to a FPGA the
control word seems to be unused, at least the Port MAC Control Register0
PortType setting bit doesn't change anything. So I can equally well use
the existing 2500BASEX mode.

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

WARNING: multiple messages have this Message-ID (diff)
From: Sascha Hauer <s.hauer@pengutronix.de>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: devicetree@vger.kernel.org, kernel@pengutronix.de,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] net: ethernet: mvneta: add support for 2.5G DRSGMII mode
Date: Tue, 9 Jun 2020 14:11:31 +0200	[thread overview]
Message-ID: <20200609121131.GJ11869@pengutronix.de> (raw)
In-Reply-To: <20200608160801.GO1551@shell.armlinux.org.uk>

On Mon, Jun 08, 2020 at 05:08:01PM +0100, Russell King - ARM Linux admin wrote:
> On Mon, Jun 08, 2020 at 09:47:16AM +0200, Sascha Hauer wrote:
> > The Marvell MVNETA Ethernet controller supports a 2.5 Gbps SGMII mode
> > called DRSGMII.
> > 
> > This patch adds a corresponding phy-mode string 'drsgmii' and parses it
> > from DT. The MVNETA then configures the SERDES protocol value
> > accordingly.
> > 
> > It was successfully tested on a MV78460 connected to a FPGA.
> 
> Digging around, this is Armada XP?  Which SoCs is this mode supported?
> There's no mention of DRSGMII in the A38x nor A37xx documentation which
> are later than Armada XP.

It's an Armada XP MV78460 in my case. I have no idea what other SoCs
this mode is supported on.

> 
> What exactly is "drsgmii"?  It can't be "double-rate" SGMII because that
> would give you 2Gbps max instead of the 1Gbps, but this gives 2.5Gbps,
> so I'm really not sure using "drsgmii" is a good idea.  It may be what
> Marvell call it, but we really need to know if there's some vendor
> neutral way to refer to it.

The abbreviation really is for "Double Rated SGMII". It seems it has 2.5
times the clock rate than ordinary SGMII. Another term I found is HSGMII
(High serial gigabit media-independent interface) which also has
2.5Gbps.

Anyway, I just learned from the paragraph you added to
Documentation/networking/phy.rst that 1000BASEX differs from SGMII in
the format of the control word. As we have a fixed link to a FPGA the
control word seems to be unused, at least the Port MAC Control Register0
PortType setting bit doesn't change anything. So I can equally well use
the existing 2500BASEX mode.

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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  reply	other threads:[~2020-06-09 12:11 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-08  7:47 [PATCH] net: ethernet: mvneta: add support for 2.5G DRSGMII mode Sascha Hauer
2020-06-08  7:47 ` Sascha Hauer
2020-06-08 14:57 ` Andrew Lunn
2020-06-08 14:57   ` Andrew Lunn
2020-06-09 12:55   ` Sascha Hauer
2020-06-09 12:55     ` Sascha Hauer
2020-06-09 13:12     ` Andrew Lunn
2020-06-09 13:12       ` Andrew Lunn
2020-06-09 13:14       ` Sascha Hauer
2020-06-09 13:14         ` Sascha Hauer
2020-06-08 16:08 ` Russell King - ARM Linux admin
2020-06-08 16:08   ` Russell King - ARM Linux admin
2020-06-09 12:11   ` Sascha Hauer [this message]
2020-06-09 12:11     ` Sascha Hauer
  -- strict thread matches above, loose matches on Subject: below --
2017-01-23 14:22 Jan Luebbe
2017-01-23 18:18 ` Andrew Lunn
     [not found]   ` <20170123181836.GO10895-g2DYL2Zd6BY@public.gmane.org>
2017-01-24  8:34     ` Jan Lübbe
2017-01-24 13:19       ` Andrew Lunn
     [not found] ` <20170123142206.5390-1-jlu-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2017-01-25 17:38   ` David Miller
     [not found]     ` <20170125.123806.790914338952471404.davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
2017-01-26  8:17       ` Jan Lübbe

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