netdev - Re: [PATCH net v2] phy: avoid unnecessary link-up delay in polling mode

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Date:   Sat, 1 Feb 2020 21:26:54 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Ivan Vecera <ivecera@...hat.com>
Cc:     poros@...hat.com, netdev@...r.kernel.org, andrew@...n.ch,
        f.fainelli@...il.com
Subject: Re: [PATCH net v2] phy: avoid unnecessary link-up delay in polling
 mode

On 01.02.2020 11:25, Ivan Vecera wrote:
> On Fri, 31 Jan 2020 21:50:48 +0100
> Heiner Kallweit <hkallweit1@...il.com> wrote:
> 
>>> 0x7949
>>> [   24.154174] xgene-mii-rgmii:03: genphy_update_link(), line: 1927, link: 0
>>>
>>> . supressed 3 same messages in T0+1,2,3s
>>>
>>> [   28.609822] xgene-mii-rgmii:03: genphy_update_link(), line: 1895, link: 0
>>> [   28.629906] xgene-mii-rgmii:03: genphy_update_link(), line: 1917, status:
>>> 0x7969
>>> ^^^^^^^^^^^^^^^ detected BMSR_ANEGCOMPLETE but not BMSR_LSTATUS
>>> [   28.644590] xgene-mii-rgmii:03: genphy_update_link(), line: 1921, status:
>>> 0x796d
>>> ^^^^^^^^^^^^^^^ here is detected BMSR_ANEGCOMPLETE and BMSR_LSTATUS
>>> [   28.658681] xgene-mii-rgmii:03: genphy_update_link(), line: 1927, link: 1
>>>   
>>
>> I see, thanks. Strange behavior of the PHY. Did you test also with other PHY's
>> whether they behave the same?
> 
> Yeah, it's strange... we could try different PHYs but anyway the double read was
> removed for polling mode to detect momentary link drops but it make sense only
> when phy->link is not 0. Thoughts?
> 
> Ivan
> 
I checked with the internal PHY of a Realtek NIC and it showed the same behavior.
So it seems that Realtek PHY's behave like this in general. Therefore I'm fine
with the patch. Just two things:
- Add details about this quirky behavior to the commit description.
- Resubmit annotated as net-next once net-next is open again. It's an improvement,
  not a fix.

Heiner