netdev - Re: [PATCH v14 2/4] phy: Add media type and speed serdes configuration interfaces

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Date:   Tue, 16 Feb 2021 15:54:35 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Steen Hegelund <steen.hegelund@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>
CC:     Vinod Koul <vkoul@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Microchip UNG Driver List <UNGLinuxDriver@...rochip.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 2/4] phy: Add media type and speed serdes
 configuration interfaces

Hi,

On 16/02/21 2:07 pm, Steen Hegelund wrote:
> 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.

Okay.. is it the same case for set_media as well?

Thanks
Kishon