linux-kernel - Re: [PATCH net v2 2/2] net: fec: Suspend and resume the PHY

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Date: Fri, 1 Mar 2024 08:10:34 +0000
From: John Ernberg <john.ernberg@...ia.se>
To: Wei Fang <wei.fang@....com>
CC: Shenwei Wang <shenwei.wang@....com>, Clark Wang <xiaoning.wang@....com>,
	dl-linux-imx <linux-imx@....com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>, Heiner Kallweit <hkallweit1@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Andrew Lunn
	<andrew@...n.ch>
Subject: Re: [PATCH net v2 2/2] net: fec: Suspend and resume the PHY

Hi Wei,

On 3/1/24 02:49, Wei Fang wrote:
>> -----Original Message-----
>> From: John Ernberg <john.ernberg@...ia.se>
>> Sent: 2024年2月29日 18:53
>> To: Wei Fang <wei.fang@....com>
>> Cc: Shenwei Wang <shenwei.wang@....com>; Clark Wang
>> <xiaoning.wang@....com>; dl-linux-imx <linux-imx@....com>; David S.
>> Miller <davem@...emloft.net>; Eric Dumazet <edumazet@...gle.com>;
>> Jakub Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>;
>> Heiner Kallweit <hkallweit1@...il.com>; netdev@...r.kernel.org;
>> linux-kernel@...r.kernel.org; John Ernberg <john.ernberg@...ia.se>
>> Subject: [PATCH net v2 2/2] net: fec: Suspend and resume the PHY
>>
>> PHYs that are always-on will not enter their low power modes otherwise as
>> they have no regulator to be powered off with.
>>
>> Since the PHY is picked up via {of_,}phy_connect() and dropped with
>> phy_disconnect() when the link is brought up and down respectively the only
>> cases were pm is needed is when the netif is running or or when the link
> nit: where
> 
>> has never been up.
>>
>> To deal with the latter case the PHY is suspended on discovery in probe,
>> since it won't be needed until link up.
>>
>> Fixes: 557d5dc83f68 ("net: fec: use mac-managed PHY PM")
> I'm not sure whether this commit should be blamed. After checking my local
> code (not the recent upstream code), fec_suspend() will make the PHY enter
> suspend mode when calling phy_stop(), the specific logic is fec_suspend() -->
> phy_stop() --> phy_state_machine() --> phy_suspend (). But the latest upstream
> code may have changed this logic. I'm sorry that I don't have time to sit down
> and look at the latest code.

I missed this flow, and also didn't see it take place when I look at the 
MDIO traffic. But the code has been there since 2013.

I will check why that isn't happening.

Thanks! // John Ernberg