netdev - Re: Ethernet: how to disable gigabit support

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Message-ID: <CAGVrzcY-euCPuU6QkpV=dYVk0CALPjngDVMbRrOt16+9AP81Lg@mail.gmail.com>
Date:	Thu, 12 Feb 2015 06:12:26 -0800
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Ethernet: how to disable gigabit support

2015-02-06 5:57 GMT-08:00 Pavel Machek <pavel@....cz>:
> On Thu 2015-02-05 14:44:55, Florian Fainelli wrote:
>> On 05/02/15 12:25, Pavel Machek wrote:
>> > Hi!
>> >
>> > This happened on more than one project: there's gigabit-capable chip,
>> > but the connector is not designed for gigabit speed.
>> >
>> > I'd like to have speed autonegotiation, but not offer gigabit (as it
>> > will not work).
>> >
>> > Is there way to do that without hacking the kernel? Should mii-tool do
>> > that?
>>
>> Since you use the PHY library, you should be able to do something like
>> this in your PHY driver prior to starting the PHY state machine:
>>
>> phydev->supported &= PHY_BASIC_FEATURES (effectively masking Gigabit
>> capability)
>
> Thanks, that did the trick.
>                                                                 Pavel
> (But still it would be nice to have a generic way of doing this,
> using something like mii-tool.)

You can also force that by setting the "max-speed" property in the
Ethernet PHY node, the PHY library will populate the supported bitmask
accordingly and remove speeds which are not supposed to be supported.

I have to admit it has been a while since I used mii-tool, so the
ioctl() side on the PHY library might be off.
--
Florian
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