Message-ID: <20130219150500.GG4390@arwen.pp.htv.fi>
Date:	Tue, 19 Feb 2013 17:05:00 +0200
From:	Felipe Balbi <balbi@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<balbi@...com>, 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

Hi,

On Tue, Feb 19, 2013 at 02:34:40PM +0000, Arnd Bergmann wrote:
> 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 ;-)

it's not so simple :-) if we must use bus_type we need to introduce all
the device/driver matching mechanism which isn't necessary with a class.

> 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.

right, but maybe we need another mechanism. If, in the long run we must
use bus_type, then eventually pwm, led, regulators, etc will all be
converted to bus_type. It will look quite weird IMHO.

Greg, can you pitch your suggestion here ? It would be great to hear
your rationale behind dropping class infrastructure, couldn't find
anything through Google and since feature-removal-schedule.txt has been
removed (without adding it to feature-removal-schedule.txt, I must add
:-) I don't know what's the idea behind removing classes.

cheers

-- 
balbi

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