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

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Message-ID: <3839600.WiC1OLF35o@flatron>
Date:	Sun, 21 Jul 2013 12:31:05 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Kishon Vijay Abraham I <kishon@...com>,
	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

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.

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"),
	/* etc... */
};

static void my_machine_init(void)
{
	/* ... */
	phy_register_lookup(my_phy_lookup, ARRAY_SIZE(my_phy_lookup));
	/* ... */
}

/* Notice nothing stuffed in platform data. */

[provider code - samsung-usbphy driver]

static int samsung_usbphy_probe(...)
{
	/* ... */
		for (i = 0; i < PHY_COUNT; ++i) {
			usbphy->phy[i].name = "phy";
			usbphy->phy[i].id = i;
			/* ... */
			ret = phy_create(&usbphy->phy);
			/* err handling */
		}
	/* ... */
}

[consumer code - s3c-hsotg driver]

static int s3c_hsotg_probe(...)
{
	/* ... */
	phy = phy_get(&pdev->dev, "otg");
	/* ... */
}

[1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/252813

Best regards,
Tomasz

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