netdev - Re: [PATCH v3 1/3] net: phy: add EXPORT_SYMBOL to phy_disable

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Date:   Tue, 20 Dec 2022 16:19:40 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Enguerrand de Ribaucourt 
        <enguerrand.de-ribaucourt@...oirfairelinux.com>
Cc:     netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
        woojung huh <woojung.huh@...rochip.com>,
        davem <davem@...emloft.net>,
        UNGLinuxDriver <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Subject: Re: [PATCH v3 1/3] net: phy: add EXPORT_SYMBOL to
 phy_disable_interrupts()

On 20.12.2022 16:02, Enguerrand de Ribaucourt wrote:
>> From: "Heiner Kallweit" <hkallweit1@...il.com>
>> To: "Enguerrand de Ribaucourt" <enguerrand.de-ribaucourt@...oirfairelinux.com>,
>> "netdev" <netdev@...r.kernel.org>
>> Cc: "Paolo Abeni" <pabeni@...hat.com>, "woojung huh"
>> <woojung.huh@...rochip.com>, "davem" <davem@...emloft.net>, "UNGLinuxDriver"
>> <UNGLinuxDriver@...rochip.com>, "Andrew Lunn" <andrew@...n.ch>, "Russell King -
>> ARM Linux" <linux@...linux.org.uk>
>> Sent: Tuesday, December 20, 2022 3:40:15 PM
>> Subject: Re: [PATCH v3 1/3] net: phy: add EXPORT_SYMBOL to
>> phy_disable_interrupts()
> 
>> On 20.12.2022 14:19, Enguerrand de Ribaucourt wrote:
>>> It seems EXPORT_SYMBOL was forgotten when phy_disable_interrupts() was
>>> made non static. For consistency with the other exported functions in
>>> this file, EXPORT_SYMBOL should be used.
> 
>> No, it wasn't forgotten. It's intentional. The function is supposed to
>> be used within phylib only.
> 
>> None of the phylib maintainers was on the addressee list of your patch.
>> Seems you didn't check with get_maintainers.pl.
> 
>> You should explain your use case to the phylib maintainers. Maybe lan78xx
>> uses phylib in a wrong way, maybe an extension to phylib is needed.
>> Best start with explaining why lan78xx_link_status_change() needs to
>> fiddle with the PHY interrupt. It would help be helpful to understand
>> what "chip" refers to in the comment. The MAC, or the PHY?
>> Does the lan78xx code assume that a specific PHY is used, and the
>> functionality would actually belong to the respective PHY driver?
> 
> Thank you for your swift reply,
> 
> The requirement to toggle the PHY interrupt in lan78xx_link_status_change() (the
> LAN7801 MAC driver) comes from a workaround by the original author which resets
> the fixed speed in the PHY when the Ethernet cable is swapped. According to his
> message, the link could not be correctly setup without this workaround.
> 
> Unfortunately, I don't have the cables to test the code without the workaround
> and it's description doesn't explain what problem happens more precisely.
> 
> The PHY the original author used is a LAN8835. The workaround code directly
> modified the interrupt configuration registers of this LAN8835 PHY within
> lan78xx_link_status_change(). This caused problems if a different PHY was used
> because the register at this address did not correspond to the interrupts
> configuration. As suggested by the lan78xx.c maintainer, a generic function
> should be used instead to toggle the interrupts of the PHY. However, it seems
> that maybe the MAC driver shouldn't meddle with the PHY's interrupts according
> to you. Would you consider this use case a valid one?
> 
So this workaround works around a silicon bug in LAN8835?
Then the code supposedly should go to the link_change_notify handler of the
Microchip PHY driver for LAN8835.
There's just a generic PHY driver for LAN88xx. Would be helpful to know
which Microchip PHY's are affected.

> Enguerrand
> 
>>> Fixes: 3dd4ef1bdbac ("net: phy: make phy_disable_interrupts() non-static")
>>> Signed-off-by: Enguerrand de Ribaucourt
>>> <enguerrand.de-ribaucourt@...oirfairelinux.com>
>>> ---
>>> drivers/net/phy/phy.c | 1 +
>>> 1 file changed, 1 insertion(+)
> 
>>> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
>>> index e5b6cb1a77f9..33250da76466 100644
>>> --- a/drivers/net/phy/phy.c
>>> +++ b/drivers/net/phy/phy.c
>>> @@ -992,6 +992,7 @@ int phy_disable_interrupts(struct phy_device *phydev)
>>> /* Disable PHY interrupts */
>>> return phy_config_interrupt(phydev, PHY_INTERRUPT_DISABLED);
>>> }
>>> +EXPORT_SYMBOL(phy_disable_interrupts);
> 
>>> /**
>>> * phy_interrupt - PHY interrupt handler