netdev - Re: [PATCH net-next] net: phy: improve link partner capability detection

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Message-ID: <dab9cd9c-1696-a6d6-e869-98b3745c0d4a@gmail.com>
Date:   Fri, 5 Apr 2019 23:20:47 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: improve link partner capability
 detection

On 05.04.2019 23:16, Heiner Kallweit wrote:
> On 05.04.2019 23:11, Florian Fainelli wrote:
>> On 4/5/19 1:51 PM, Heiner Kallweit wrote:
>>> On 05.04.2019 22:43, Andrew Lunn wrote:
>>>>> Right. BMSR_ESTATEN should not be set on a Fast PHY. Handling of this
>>>>> case didn't change.
>>>>>
>>>>>> A Fast MAC connected to a Giga PHY. The MAC driver will of used
>>>>>> phy_set_max_speed() to indicate its limits. In that case, MII_STAT1000
>>>>>> does exist and we should report what the peer is advertising.
>>>>>>
>>>>> That's what we're doing now with this patch.
>>>>
>>>> Hi Heiner
>>>>
>>>> What i don't get is why we need to do anything based on the MAC. All
>>>> we need to do is look at BMSR_ESTATEN, and from that decided if we
>>>> should look at MII_STAT1000 or not. When reporting what the peer can
>>>> do, we should not care what the local MAC can do.
>>>>
>>> Do we have a misunderstanding? What you describe is exactly what we're
>>> doing now. BMSR_ESTATEN is read by genphy_read_abilities().
>>> I just don't want to read BMSR whenever genphy_read_status() is called.
>>
>> You have to read the BMSR to determine the link status anyway, did you
>> mean: have to check BMSR_ESTATEN whenever genphy_read_status() is called?
>>
> I would have to add extra logic to propagate BMSR_ESTATEN  from
> genphy_update_link() to genphy_read_status(). BMSR_ESTATEN has a fixed
> value and therefore it's sufficient to read it initially.
> 
In addition: BMSR_ESTATEN being set isn't a guarantee yet that the PHY
supports gigabit. Still in MII_ESTATUS the gigabit bits couldn't be set.
A Fast PHY could use some IP which is gigabit-prepared.
I don't know if such a PHY exists, but it would be totally compliant
with C22.