netdev - Re: [PATCH v2] cpsw: ethtool: add support for getting/setting EEE registers

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Message-ID: <2b4912e6-c380-b2bd-762a-d1da2b0a7d82@st.com>
Date:   Fri, 2 Dec 2016 10:11:10 +0100
From:   Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Yegor Yefremov <yegorslists@...glemail.com>
CC:     netdev <netdev@...r.kernel.org>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "N, Mugunthan V" <mugunthanvnm@...com>,
        Rami Rosen <roszenrami@...il.com>,
        Fabrice GASNIER <fabrice.gasnier@...com>
Subject: Re: [PATCH v2] cpsw: ethtool: add support for getting/setting EEE
 registers

Hi Florian
sorry for my delay.

On 11/24/2016 7:23 PM, Florian Fainelli wrote:
> +Peppe,
>
> Le 24/11/2016 à 07:38, Andrew Lunn a écrit :
>>> As for enabling advertising and correct working of cpsw do you mean it
>>> would be better to disable EEE in any PHY on cpsw initialization as
>>> long as cpsw doesn't provide support for EEE?
>>>
>>> We observe some strange behavior with our gigabit PHYs and a link
>>> partner in a EEE-capable unmanaged NetGear switch. Disabling
>>> advertising seems to help. Though we're still investigating the issue.
>>
>> Hi Florian
>>
>> Am i right in saying, a PHY should not advertise EEE until the MAC
>> driver calls phy_init_eee(), indicating the MAC supports EEE?
>
> You would think so, but I don't see how this could possibly work if that
> was not the case already, see below.
>
>>
>> If so, it looks like we need to change a few of the PHY drivers, in
>> particular, the bcm-*.c.
>
> The first part that bcm-phy-lib.c does is make sure that EEE is enabled
> such that this gets reflected in MDIO_PCS_EEE_ABLE, without this, we
> won't be able to pass the first test in phy_init_eee(). The second part
> is to advertise EEE such that this gets reflected in MDIO_AN_EEE_ADV,
> also to make sure that we can pass the second check in phy_init_eee().
>
> Now, looking at phy_init_eee(), and what stmmac does (and bcmgenet,
> copied after stmmac), we need to somehow, have EEE advertised for
> phy_init_eee() to succeed, prepare the MAC to support EEE, and finally
> conclude with a call to phy_ethtool_set_eee(), which writes to the
> MDIO_AN_EEE_ADV register, and concludes the EEE auto-negotiated process.
> Since we already have EEE advertised, we are essentially just checking
> that the EEE advertised settings and the LP advertised settings actually
> do match, so it sounds like the final call to phy_ethtool_set_eee() is
> potentially useless if the resolved advertised and link partner
> advertised settings already match...
>
> So it sounds like at least, the first time you try to initialize EEE, we
> should start with EEE not advertised, and then, if we have EEE enabled
> at some point, and we re-negotiate the link parameters, somehow
> phy_init_eee() does a right job for that.
>
> Peppe, any thoughts on this?

I share what you say.

In sum, the EEE management inside the stmmac is:

- the driver looks at own HW cap register if EEE is supported

     (indeed the user could keep disable EEE if bugged on some HW
      + Alex, Fabrice: we had some patches for this to propose where we
              called the phy_ethtool_set_eee to disable feature at phy
              level

- then the stmmac asks PHY layer to understand if transceiver and
   partners are EEE capable.

- If all matches the EEE is actually initialized.

the logic above should be respected when use ethtool, hmm, I will
check the stmmac_ethtool_op_set_eee asap.

Hoping this is useful

Regards
Peppe