linux-kernel - Re: [PATCH v2 0/5] Generic PHY Framework

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Message-Id: <201302191434.40495.arnd@arndb.de>
Date:	Tue, 19 Feb 2013 14:34:40 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	balbi@...com
Cc:	kishon <kishon@...com>, rob@...dley.net, tony@...mide.com,
	linux@....linux.org.uk, eballetbo@...il.com, javier@...hile0.org,
	gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
	mchehab@...hat.com, cesarb@...arb.net, davem@...emloft.net,
	santosh.shilimkar@...com, broonie@...nsource.wolfsonmicro.com,
	swarren@...dia.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-omap@...r.kernel.org, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 0/5] Generic PHY Framework

On Tuesday 19 February 2013, Felipe Balbi wrote:
> On Tue, Feb 19, 2013 at 12:33:54PM +0000, Arnd Bergmann wrote:
> > > Currently drivers/phy and drivers/net/phy are independent and are not 
> > > related to each other. There are some fundamental differences on how 
> > > these frameworks work. IIUC, the *net* uses bus layer (MDIO bus) to 
> > > match a PHY device with a PHY driver and the Ethernet device uses the 
> > > bus layer to get the PHY.
> > > The Generic PHY Framework however doesn't have any bus layer. The PHY 
> > > should be like any other Platform Devices and Drivers and the framework 
> > > will provide some APIs to register with the framework. And there are 
> > > other APIs which any controller can use to get the PHY (for e.g., in the 
> > > case of dt boot, it can use phandle to get a reference to the PHY).
> > 
> > Hmm, I think the use of a bus_type for a PHY actually sounds quite
> > appropriate. The actual PHY device would then be a child of the
> 
> really ? I'm not so sure, the *bus* used by the PHY is ULPI, UTMI,
> UTMI+, PIP3, I2C, etc... adding another 'fake' bus representation is a
> bit overkill IMO.
> 
> Imagine an I2C-controlled PHY driver like isp1301, that driver will have
> to register i2c_driver and phy_driver, which looks weird to me. If the
> only substitute for class is a bus, we can't drop classes just yet, I'm
> afraid.
> 
> Imagine a regulator bus, a pwm bus, an LED bus etc. They don't make
> sense IMHO.

It's a fine line, but I think a phy is something that resembles a device
more than an LED does. When I read patch 1, I also noticed and commented
on the fact that it does use a 'class'. Now, according to Greg, we should
use 'bus_type' instead of 'class' in new code. I originally disagreed with
that concept, but he's the boss here and it's good if he has a vision
how things should be lined out.

In practice, there is little difference between a 'bus_type' and a 'class',
so just replace any instance of the former with the latter in your head
when reading the code ;-)
I understand that there is not a real common bus here, and the bus_type
infrastructure would basically be used as a way to represent each PHY
in sysfs and provide a way to enumerate and look them up inside of the
kernel.

	Arnd
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