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

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Date:   Fri, 31 Jan 2020 10:42:05 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dan Murphy <dmurphy@...com>, andrew@...n.ch, hkallweit1@...il.com,
        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 1/31/20 10:29 AM, Dan Murphy wrote:
> Florian
> 
> On 1/31/20 11:49 AM, Florian Fainelli wrote:
>> On 1/31/20 7:11 AM, 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.
>> OK, but why and how does that optimization work exactly?
> 
> I described this in the cover letter.  And it is explained in the data
> sheet Section 8.4.6.6

Sorry I complete missed that and just focused on the patch, you should
consider not providing a cover letter for a single patch, and especially
not when the cover letter contains more information than the patch
commit message itself.

> 
>>   Departing from
>> the BMSR reads means you possibly are going to introduce bugs and/or
>> incomplete information. For instance, you set phydev->pause and
>> phydev->asym_pause to 0 now, is there no way to extract what the link
>> partner has advertised?
> 
> I was using the marvel.c as my template as it appears to have a separate
> status register as well.
> 
> Instead of setting those bits in the call back I can call the
> genphy_read_status then override the duplex and speed based on the
> physts register like below.  This way link status and pause values can
> be updated and then we can update the speed and duplex settings.
> 
>       ret = genphy_read_status(phydev);
>     if (ret)
>         return ret;
> 
>     if (status < 0)
>         return status;
> 
>     if (status & DP83867_PHYSTS_DUPLEX)
>         phydev->duplex = DUPLEX_FULL;
>     else
>         phydev->duplex = DUPLEX_HALF;
> 
>     if (status & DP83867_PHYSTS_1000)
>         phydev->speed = SPEED_1000;
>     else if (status & DP83867_PHYSTS_100)
>         phydev->speed = SPEED_100;
>     else
>         phydev->speed = SPEED_10;
> 

OK, but what if they disagree, are they consistently latched with
respect to one another?

> 
>>> With this bit set the PHY will auto negotiate and report the link
>>> parameters in the PHYSTS register and not in the BMCR.
>> That should be BMSR, the BMCR is about control, not status.
> 
> OK.
> 
> Dan
> 


-- 
Florian