netdev - Re: [PATCH net-next 10/11] net: dsa: mv88e6xxx: remove EEE support

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Message-ID: <17c26dee-c285-4dd5-1be0-286c0126d4db@gmail.com>
Date:   Tue, 1 Aug 2017 09:33:52 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...oirfairelinux.com,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 10/11] net: dsa: mv88e6xxx: remove EEE support

On 08/01/2017 09:06 AM, Andrew Lunn wrote:
> On Tue, Aug 01, 2017 at 11:36:13AM -0400, Vivien Didelot wrote:
>> Hi Andrew,
>>
>> Andrew Lunn <andrew@...n.ch> writes:
>>
>>> On Mon, Jul 31, 2017 at 06:17:18PM -0400, Vivien Didelot wrote:
>>>> The PHY's EEE settings are already accessed by the DSA layer through the
>>>> Marvell PHY driver and there is nothing to be done for switch's MACs.
>>>
>>> I'm confused, or missing something. Does not patch #1 mean that if the
>>> DSA driver does not have a set_eee function, we always return -ENODEV
>>> in slave.c?
>>
>> If there is a PHY, phy_init_eee (if eee_enabled is true) and
>> phy_ethtool_set_eee is called. If there is a .set_eee op, it is
>> called. If both are absent, -ENODEV is returned.
> 
> O.K, i don't think that is correct. EEE should only be enabled if both
> the MAC and the PHY supports it. We need some way for the MAC to
> indicate it does not support EEE.

If the MAC does not support EEE but the PHY does I think you can still
allow EEE to be advertised and enabled, you just won't have the MAC be
able to leverage the power savings that EEE brings. AFAICT this is still
a valid mode whereby the PHY is put in a lower power mode, just not the
whole transmit path (MAC + PHY).

> 
> If set_eee is optional the meaning of a NULL pointer is that the MAC
> does support EEE. So for mv88e6060, lan9303, microchip and mt7530
> which currently don't support EEE, you need to add a set_eee which
> returns -ENODEV.
> 
> Having to implement the op to say you don't implement the feature just
> seems wrong.

If it is truly optional then we can either request drivers to implement
it and return something agreed upon, or just not implementing it means
we might be able to do EEE only at the PHY level.
-- 
Florian