linux-kernel - Re: [PATCH] net: usb: lan78xx: add weak dependency with micrel phy module

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Message-ID: <a520ee4da331c8edb99f2c14d22a3531@manjaro.org>
Date: Sun, 28 Jul 2024 16:10:57 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Jose Ignacio Tornos Martinez <jtornosm@...hat.com>,
 UNGLinuxDriver@...rochip.com, davem@...emloft.net, edumazet@...gle.com,
 f.fainelli@...il.com, gregkh@...uxfoundation.org, kuba@...nel.org,
 linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org, lucas.demarchi@...el.com, masahiroy@...nel.org,
 mcgrof@...nel.org, netdev@...r.kernel.org, pabeni@...hat.com,
 woojung.huh@...rochip.com
Subject: Re: [PATCH] net: usb: lan78xx: add weak dependency with micrel phy
 module

Hello Andrew,

On 2024-07-28 01:29, Andrew Lunn wrote:
>> Before going into explaining my viewpoint, could someone, please, 
>> clarify
>> which LAN78xx USB-to-Ethernet bridge does this apply to?  I already 
>> had
>> a look at a few LAN78xx datasheets, and I'm not sure how the external 
>> PHY
>> becomes exposed over the USB interface, so it needs a driver.
> 
> https://elixir.bootlin.com/linux/v6.10/source/drivers/net/usb/lan78xx.c#L2049
> 
> This is creating an MDIO bus device. The MDIO bus will be scanned and
> PHYs on the bus found. There are then a few calls to phy_find_first()
> which will get the PHY.
> 
> The code itself looks pretty broken, it is directly accessing PHY
> registers, which a MAC driver should not do. That is a layering
> violation.

Thanks for the clarification.

Basically, the way I see it, weakdeps are the right solution for the
problem at hand, i.e. for the generation of the initial ramdisk with
all the possible PHY driver modules.  However, I don't think that some
automagical generation of the associated MODULE_WEAKDEP() statements
is the way to go.  Instead, all those statements should be added by
hand to the lan78xx driver, making sure that each PHY is tested and
validated beforehand.