linux-kernel - Re: [PATCH net-master 1/1] net: phy: dp83867: Add speed optimization feature

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Message-ID: <2116231e-2373-6511-da06-32ea01266b49@gmail.com>
Date:   Fri, 31 Jan 2020 20:57:14 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dan Murphy <dmurphy@...com>,
        Heiner Kallweit <hkallweit1@...il.com>, andrew@...n.ch,
        bunk@...nel.org
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, grygorii.strashko@...com
Subject: Re: [PATCH net-master 1/1] net: phy: dp83867: Add speed optimization
 feature



On 1/31/2020 5:30 PM, Dan Murphy wrote:
> Heiner
> 
> On 1/31/20 2:56 PM, Heiner Kallweit wrote:
>> On 31.01.2020 16:11, Dan Murphy wrote:
>>> Set the speed optimization bit on the DP83867 PHY.
>>> This feature can also be strapped on the 64 pin PHY devices
>>> but the 48 pin devices do not have the strap pin available to enable
>>> this feature in the hardware.  PHY team suggests to have this bit set.
>>>
>> It's ok to enable downshift by default, however it would be good to
>> make it configurable. Best implement the downshift tunable, you can
>> use the Marvell PHY driver as reference.
>> Can the number of attempts until downshifts happens be configured?
> 
> Yes we can tune the number of attempts it makes to negotiate 1000Mbps
> before enabling the speed optimization.  But why would we need to
> configure the number of attempts currently it is defaulted to 4.  Is
> there a use case for this level of configurability?

Some customers may prefer a fast(er) link re-negotiation once they know
the cabling is faulty or sub-optimal. The default is usually fine, and
if you want to support the downshift ethtool tunable when net-next opens
back up, that would be a welcome addition.
-- 
Florian