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

Hi Kishon,

On Tue, 2021-02-16 at 15:54 +0530, Kishon Vijay Abraham I wrote:

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Hi,

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

quoted

Hi Andrew and Kishon,

On Mon, 2021-02-15 at 15:07 +0100, Andrew Lunn wrote:

quoted

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On Mon, Feb 15, 2021 at 05:25:10PM +0530, Kishon Vijay Abraham I
wrote:

quoted

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?

Yes, but in the media type case, we should be able to get the type from
the DAC cable EPPROM information as mentioned by Andrew, so human
intervention should not be needed.

Thanks
Kishon

Thanks for your comments.

-- 
BR
Steen

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steen.hegelund@microchip.com