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

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Date:   Fri, 5 Apr 2019 23:52:12 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        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 23:38, Heiner Kallweit wrote:
> On 05.04.2019 23:27, Andrew Lunn wrote:
>>> +	if (linkmode_test_bit(ETHTOOL_LINK_MODE_1000baseT_Half_BIT,
>>> +			      phydev->supported))
>>> +		phydev->is_gigabit_capable = 1;
>>> +	if (linkmode_test_bit(ETHTOOL_LINK_MODE_1000baseT_Full_BIT,
>>> +			      phydev->supported))
>>> +		phydev->is_gigabit_capable = 1;
>>> +
>>
>> What i'm trying to get at is, why do we need this bit of the patch?
>> Why do we need this flag? The hardware should tell us if it can do
>> gigabit.
>>
> The code to query BMSR_ESTATEN and MII_ESTATUS is in genphy_read_status.
> However we also have to cover the case that this function isn't used.
> Therefore I query phydev->supported before the speed could be limited.
> (relying on the PHY driver not lying about gigabit capability)
> This part of the patch is directly before of_set_phy_supported().
> 
> I just see that we can re-use is_gigabit_capable also in
> genphy_config_advert.
> 
> Of course I can read in every place the hardware for gigabit support.
> But IMO this creates unnecessary code duplication.
> 
I just see that we can reuse is_gigabit_capable also in
genphy_config_advert().

And when checking occurrences of BMSR_ESTATEN there seems to be more
work waiting: In swphy BMSR_ESTATEN is set, but MII_ESTATUS isn't
configured. It just works by chance becausing reading this register
returns the default 0xffff.

>> 	Andrew
>>
> Heiner
>