linux-kernel - Re: [PATCH 01/15] drivers: phy: add generic PHY framework

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Date:	Sun, 21 Jul 2013 13:12:07 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Kishon Vijay Abraham I <kishon@...com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	kyungmin.park@...sung.com, balbi@...com, jg1.han@...sung.com,
	s.nawrocki@...sung.com, kgene.kim@...sung.com,
	grant.likely@...aro.org, tony@...mide.com, arnd@...db.de,
	swarren@...dia.com, devicetree-discuss@...ts.ozlabs.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-media@...r.kernel.org,
	linux-fbdev@...r.kernel.org, akpm@...ux-foundation.org,
	balajitk@...com, george.cherian@...com, nsekhar@...com
Subject: Re: [PATCH 01/15] drivers: phy: add generic PHY framework

On Sunday 21 of July 2013 16:37:33 Kishon Vijay Abraham I wrote:
> Hi,
> 
> On Sunday 21 July 2013 04:01 PM, Tomasz Figa wrote:
> > Hi,
> > 
> > On Saturday 20 of July 2013 19:59:10 Greg KH wrote:
> >> On Sat, Jul 20, 2013 at 10:32:26PM -0400, Alan Stern wrote:
> >>> On Sat, 20 Jul 2013, Greg KH wrote:
> >>>>>>> That should be passed using platform data.
> >>>>>> 
> >>>>>> Ick, don't pass strings around, pass pointers.  If you have
> >>>>>> platform
> >>>>>> data you can get to, then put the pointer there, don't use a
> >>>>>> "name".
> >>>>> 
> >>>>> I don't think I understood you here :-s We wont have phy pointer
> >>>>> when we create the device for the controller no?(it'll be done in
> >>>>> board file). Probably I'm missing something.
> >>>> 
> >>>> Why will you not have that pointer?  You can't rely on the "name"
> >>>> as
> >>>> the device id will not match up, so you should be able to rely on
> >>>> the pointer being in the structure that the board sets up, right?
> >>>> 
> >>>> Don't use names, especially as ids can, and will, change, that is
> >>>> going
> >>>> to cause big problems.  Use pointers, this is C, we are supposed to
> >>>> be
> >>>> doing that :)
> >>> 
> >>> Kishon, I think what Greg means is this:  The name you are using
> >>> must
> >>> be stored somewhere in a data structure constructed by the board
> >>> file,
> >>> right?  Or at least, associated with some data structure somehow.
> >>> Otherwise the platform code wouldn't know which PHY hardware
> >>> corresponded to a particular name.
> >>> 
> >>> Greg's suggestion is that you store the address of that data
> >>> structure
> >>> in the platform data instead of storing the name string.  Have the
> >>> consumer pass the data structure's address when it calls phy_create,
> >>> instead of passing the name.  Then you don't have to worry about two
> >>> PHYs accidentally ending up with the same name or any other similar
> >>> problems.
> >> 
> >> Close, but the issue is that whatever returns from phy_create()
> >> should
> >> then be used, no need to call any "find" functions, as you can just
> >> use
> >> the pointer that phy_create() returns.  Much like all other class api
> >> functions in the kernel work.
> > 
> > I think there is a confusion here about who registers the PHYs.
> > 
> > All platform code does is registering a platform/i2c/whatever device,
> > which causes a driver (located in drivers/phy/) to be instantiated.
> > Such drivers call phy_create(), usually in their probe() callbacks,
> > so platform_code has no way (and should have no way, for the sake of
> > layering) to get what phy_create() returns.
> 
> right.
> 
> > IMHO we need a lookup method for PHYs, just like for clocks,
> > regulators, PWMs or even i2c busses because there are complex cases
> > when passing just a name using platform data will not work. I would
> > second what Stephen said [1] and define a structure doing things in a
> > DT-like way.
> > 
> > Example;
> > 
> > [platform code]
> > 
> > static const struct phy_lookup my_phy_lookup[] = {
> > 
> > 	PHY_LOOKUP("s3c-hsotg.0", "otg", "samsung-usbphy.1", "phy.2"),
> 
> The only problem here is that if *PLATFORM_DEVID_AUTO* is used while
> creating the device, the ids in the device name would change and
> PHY_LOOKUP wont be useful.

I don't think this is a problem. All the existing lookup methods already 
use ID to identify devices (see regulators, clkdev, PWMs, i2c, ...). You 
can simply add a requirement that the ID must be assigned manually, 
without using PLATFORM_DEVID_AUTO to use PHY lookup.

Best regards,
Tomasz

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