Message-ID: <20130219161712.GB5736@arwen.pp.htv.fi>
Date:	Tue, 19 Feb 2013 18:17:12 +0200
From:	Felipe Balbi <balbi@...com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
CC:	<balbi@...com>, Arnd Bergmann <arnd@...db.de>,
	<linux-usb@...r.kernel.org>, <linux@....linux.org.uk>,
	<mchehab@...hat.com>, <davem@...emloft.net>, <tony@...mide.com>,
	<gregkh@...uxfoundation.org>,
	<broonie@...nsource.wolfsonmicro.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, kishon <kishon@...com>,
	<eballetbo@...il.com>, <santosh.shilimkar@...com>,
	<linux-arm-kernel@...ts.infradead.org>, <rob@...dley.net>,
	<netdev@...r.kernel.org>, <swarren@...dia.com>,
	<javier@...hile0.org>, <linux-omap@...r.kernel.org>,
	<akpm@...ux-foundation.org>, <cesarb@...arb.net>
Subject: Re: [PATCH v2 0/5] Generic PHY Framework

Hi,

On Tue, Feb 19, 2013 at 05:07:09PM +0100, Marc Kleine-Budde wrote:
> On 02/19/2013 04:05 PM, Felipe Balbi wrote:
> > 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.
> 
> You have the code for phy <-> device matching in your framework anyway.
> Using the bus infrastructure brings changes the open coded matching into
> bus callbacks.

it's not the same thing. Current matching is just to figure out which
phy belongs to which user. The bus matching rules are to bind a device
with its driver, but that part has been taken care of by the underlying
control bus used by the phy, be it i2c, spi, or whatever else.

-- 
balbi

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