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

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Message-ID: <Y6HfK7bnkL2uyp3m@shell.armlinux.org.uk>
Date:   Tue, 20 Dec 2022 16:13:31 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Enguerrand de Ribaucourt 
        <enguerrand.de-ribaucourt@...oirfairelinux.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        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>
Subject: Re: [PATCH v3 1/3] net: phy: add EXPORT_SYMBOL to
 phy_disable_interrupts()

Hi,

On Tue, Dec 20, 2022 at 10:02:56AM -0500, 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?

This sounds to me like you're just trying to get a workaround merged
upstream using a different approach, but you can't actually test to
see whether it does work or not. Would that be a fair assessment?

Do you know anyone who would be able to test? If not, I would suggest
not trying to upstream code for a workaround that can't be tested as
working.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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