netdev - Re: [PATCH net] amd-xgbe: read STAT1 register twice to get correct value

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Message-ID: <d6c6b06f-4f90-62da-7774-02b737198ce0@amd.com>
Date: Fri, 15 Sep 2023 14:18:55 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Andrew Lunn <andrew@...n.ch>, Raju Rangoju <Raju.Rangoju@....com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, Shyam-sundar.S-k@....com
Subject: Re: [PATCH net] amd-xgbe: read STAT1 register twice to get correct
 value



On 9/15/23 07:41, Andrew Lunn wrote:
> On Thu, Sep 14, 2023 at 09:49:44AM +0530, Raju Rangoju wrote:
>> Link status is latched low, so read once to clear
>> and then read again to get current state.
> 
> I don't know about your PHY implementation, but within phylib and
> Linux PHY drivers, this is considered wrong. You loose out on being
> notified of the link going down and then back up again. Or up and then
> down again.
> 
> But since this is not a Linux PHY driver, you are free to do whatever
> you want...
> 
> Also, i believe it is latched, not latched low. So i think your commit
> message is wrong. You should probably check with IEEE 802.3 clause 22.

Granted I have an old version of IEEE 802.3, but "Table 22-8 - Status 
register bit definitions" has:

1.2	Link Status	1 = link is up	0 = link is down	RO/LL

So latched low.

Thanks,
Tom

> 
>      Andrew
>