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Message-ID: <d5b3ccf9df1968671baadcd3c7a5e068d48867c5.camel@microchip.com>
Subject: Re: [PATCH v14 2/4] phy: Add media type and speed serdes
 configuration interfaces
From:   Steen Hegelund <steen.hegelund@microchip.com>
To:     Andrew Lunn <andrew@lunn.ch>,
        Kishon Vijay Abraham I <kishon@ti.com>
CC:     Vinod Koul <vkoul@kernel.org>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Lars Povlsen <lars.povlsen@microchip.com>,
        Bjarni Jonasson <bjarni.jonasson@microchip.com>,
        Microchip UNG Driver List <UNGLinuxDriver@microchip.com>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Date:   Tue, 16 Feb 2021 09:37:56 +0100
In-Reply-To: <YCqAMUfinMsnZnrq@lunn.ch>
References: <20210210085255.2006824-1-steen.hegelund@microchip.com>
         <20210210085255.2006824-3-steen.hegelund@microchip.com>
         <04d91f6b-775a-8389-b813-31f7b4a778cb@ti.com>
         <ffa00a2bf83ffa21ffdc61b380ab800c31f8cf28.camel@microchip.com>
         <704b850f-9345-2e36-e84b-b332fed22270@ti.com> <YCqAMUfinMsnZnrq@lunn.ch>
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Hi Andrew and Kishon,

On Mon, 2021-02-15 at 15:07 +0100, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you
> know the content is safe
> 
> On Mon, Feb 15, 2021 at 05:25:10PM +0530, Kishon Vijay Abraham I
> wrote:
> > Okay. Is it going to be some sort of manual negotiation where the
> > Ethernet controller invokes set_speed with different speeds? Or the
> > Ethernet controller will get the speed using some out of band
> > mechanism
> > and invokes set_speed once with the actual speed?
> 
> Hi Kishon
> 
> There are a few different mechanism possible.
> 
> The SFP has an EEPROM which contains lots of parameters. One is the
> maximum baud rate the module supports. PHYLINK will combine this
> information with the MAC capabilities to determine the default speed.
> 
> The users can select the mode the MAC works in, e.g. 1000BaseX vs
> 2500BaseX, via ethtool -s. Different modes needs different speeds.
> 
> Some copper PHYs will change there host side interface baud rate when
> the media side interface changes mode. 10GBASE-X for 10G copper,
> 5GBase-X for 5G COPPER, 2500Base-X for 2.5G copper, and SGMII for
> old school 10/100/1G Ethernet.
> 
> Mainline Linux has no support for it, but some 'vendor crap' will do
> a
> manual negotiation, simply trying different speeds and see if the
> SERDES establishes link. There is nothing standardised for this, as
> far as i know.
> 
>     Andrew

Yes, in case I mention the only way to ensure communication is human
intervention to set the speed to the highest common denominator.

BR
Steen