netdev - Re: [PATCH net v2 2/2] net: dsa: mt7530: fix disabling EEE on failure on MT7531 and MT7988

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Date: Tue, 26 Mar 2024 12:19:40 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: Paolo Abeni <pabeni@...hat.com>, Daniel Golle <daniel@...rotopia.org>,
 DENG Qingfang <dqfext@...il.com>, Sean Wang <sean.wang@...iatek.com>,
 Andrew Lunn <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>,
 Vladimir Oltean <olteanv@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 René van Dorst <opensource@...rst.com>,
 Russell King <linux@...linux.org.uk>,
 SkyLake Huang <SkyLake.Huang@...iatek.com>,
 Heiner Kallweit <hkallweit1@...il.com>
Cc: Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
 mithat.guner@...ont.com, erkin.bozoglu@...ont.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net v2 2/2] net: dsa: mt7530: fix disabling EEE on failure
 on MT7531 and MT7988

On 26.03.2024 12:02, Paolo Abeni wrote:
> On Thu, 2024-03-21 at 19:29 +0300, Arınç ÜNAL via B4 Relay wrote:
>> From: Arınç ÜNAL <arinc.unal@...nc9.com>
>>
>> The MT7531_FORCE_EEE1G and MT7531_FORCE_EEE100 bits let the
>> PMCR_FORCE_EEE1G and PMCR_FORCE_EEE100 bits determine the 1G/100 EEE
>> abilities of the MAC. If MT7531_FORCE_EEE1G and MT7531_FORCE_EEE100 are
>> unset, the abilities are left to be determined by PHY auto polling.
>>
>> The commit 40b5d2f15c09 ("net: dsa: mt7530: Add support for EEE features")
>> made it so that the PMCR_FORCE_EEE1G and PMCR_FORCE_EEE100 bits are set on
>> mt753x_phylink_mac_link_up(). But it did not set the MT7531_FORCE_EEE1G and
>> MT7531_FORCE_EEE100 bits. Because of this, EEE will be enabled on the
>> switch MACs by polling the PHY, regardless of the result of phy_init_eee().
>>
>> Define these bits and add them to MT7531_FORCE_MODE which is being used by
>> the subdriver. With this, EEE will be prevented from being enabled on the
>> switch MACs when phy_init_eee() fails.
>>
>> Fixes: 40b5d2f15c09 ("net: dsa: mt7530: Add support for EEE features")
>> Signed-off-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> 
> If I read the past discussion correctly, this is a potential issue
> found by code inspection and never producing problem in practice, am I
> correct?
> 
> If so I think it will deserve a 3rd party tested-by tag or similar to
> go in.
> 
> If nobody could provide such feedback in a little time, I suggest to
> drop this patch and apply only 1/2.

Whether a problem would happen in practice depends on when phy_init_eee()
fails, meaning it returns a negative non-zero code. I requested Russell to
review this patch to shed light on when phy_init_eee() would return a
negative non-zero code so we have an idea whether this patch actually fixes
a problem.

Arınç