Message-ID: <1769609.rbAYfG9ir3@flatron>
Date:	Tue, 23 Jul 2013 23:05:48 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Mark Brown <broonie@...nel.org>, Tomasz Figa <t.figa@...sung.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Alan Stern <stern@...land.harvard.edu>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	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@...r.kernel.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,
	olof@...om.net, Stephen Warren <swarren@...dotorg.org>,
	b.zolnierkie@...sung.com,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 01/15] drivers: phy: add generic PHY framework

On Tuesday 23 of July 2013 13:50:07 Greg KH wrote:
> On Tue, Jul 23, 2013 at 10:07:52PM +0200, Tomasz Figa wrote:
> > On Tuesday 23 of July 2013 12:44:23 Greg KH wrote:
> > > On Tue, Jul 23, 2013 at 08:31:05PM +0100, Mark Brown wrote:
> > > > > You don't "know" the id of the device you are looking up, due to
> > > > > multiple devices being in the system (dynamic ids, look back
> > > > > earlier
> > > > > in
> > > > > this thread for details about that.)
> > > > 
> > > > I got copied in very late so don't have most of the thread I'm
> > > > afraid,
> > > > I did try looking at web archives but didn't see a clear problem
> > > > statement.  In any case this is why the APIs doing lookups do the
> > > > lookups in the context of the requesting device - devices ask for
> > > > whatever name they use locally.
> > > 
> > > What do you mean by "locally"?
> > > 
> > > The problem with the api was that the phy core wanted a id and a
> > > name to create a phy, and then later other code was doing a
> > > "lookup" based on the name and id (mushed together), because it
> > > "knew" that this device was the one it wanted.
> > > 
> > > Just like the clock api, which, for multiple devices, has proven to
> > > cause problems.  I don't want to see us accept an api that we know
> > > has
> > > issues in it now, I'd rather us fix it up properly.
> > > 
> > > Subsystems should be able to create ids how ever they want to, and
> > > not
> > > rely on the code calling them to specify the names of the devices
> > > that
> > > way, otherwise the api is just too fragile.
> > > 
> > > I think, that if you create a device, then just carry around the
> > > pointer to that device (in this case a phy) and pass it to whatever
> > > other code needs it.  No need to do lookups on "known names" or
> > > anything else, just normal pointers, with no problems for multiple
> > > devices, busses, or naming issues.
> > 
> > PHY object is not a device, it is something that a device driver
> > creates (one or more instances of) when it is being probed.
> 
> But you created a 'struct device' for it, so I think of it as a "device"
> be it "virtual" or "real" :)

Keep in mind that those virtual devices are created by PHY driver bound to 
a real device and one real device can have multiple virtual devices behind 
it.

> > You don't have a clean way to export this PHY object to other driver,
> > other than keeping this PHY on a list inside PHY core with some
> > well-known ID (e.g. device name + consumer port name/index, like in
> > regulator core) and then to use this well-known ID inside consumer
> > driver as a lookup key passed to phy_get();
> > 
> > Actually I think for PHY case, exactly the same way as used for
> > regulators might be completely fine:
> > 
> > 1. Each PHY would have some kind of platform, non-unique name, that is
> > just used to print some messages (like the platform/board name of a
> > regulator).
> > 2. Each PHY would have an array of consumers. Consumer specifier would
> > consist of consumer device name and consumer port name - just like in
> > regulator subsystem.
> > 3. PHY driver receives an array of, let's say, phy_init_data inside
> > its
> > platform data that it would use to register its PHYs.
> > 4. Consumer drivers would have constant consumer port names and
> > wouldn't receive any information about PHYs from platform code.
> > 
> > Code example:
> > 
> > [Board file]
> > 
> > static const struct phy_consumer_data usb_20_phy0_consumers[] = {
> > 
> > 	{
> > 	
> > 		.devname = "foo-ehci",
> > 		.port = "usbphy",
> > 	
> > 	},
> > 
> > };
> > 
> > static const struct phy_consumer_data usb_20_phy1_consumers[] = {
> > 
> > 	{
> > 	
> > 		.devname = "foo-otg",
> > 		.port = "otgphy",
> > 	
> > 	},
> > 
> > };
> > 
> > static const struct phy_init_data my_phys[] = {
> > 
> > 	{
> > 	
> > 		.name = "USB 2.0 PHY 0",
> > 		.consumers = usb_20_phy0_consumers,
> > 		.num_consumers = ARRAY_SIZE(usb_20_phy0_consumers),
> > 	
> > 	},
> > 	{
> > 	
> > 		.name = "USB 2.0 PHY 1",
> > 		.consumers = usb_20_phy1_consumers,
> > 		.num_consumers = ARRAY_SIZE(usb_20_phy1_consumers),
> > 	
> > 	},
> > 	{ }
> > 
> > };
> > 
> > static const struct platform_device usb_phy_pdev = {
> > 
> > 	.name = "foo-usbphy",
> > 	.id = -1,
> > 	.dev = {
> > 	
> > 		.platform_data = my_phys,
> > 	
> > 	},
> > 
> > };
> > 
> > [PHY driver]
> > 
> > static int foo_usbphy_probe(pdev)
> > {
> > 
> > 	struct foo_usbphy *foo;
> > 	struct phy_init_data *init_data = pdev->dev.platform_data;
> > 	/* ... */
> > 	// for each PHY in init_data {
> > 	
> > 		phy_register(&foo->phy[i], &init_data[i]);
> > 	
> > 	// }
> > 	/* ... */
> > 
> > }
> > 
> > [EHCI driver]
> > 
> > static int foo_ehci_probe(pdev)
> > {
> > 
> > 	struct phy *phy;
> > 	/* ... */
> > 	phy = phy_get(&pdev->dev, "usbphy");
> > 	/* ... */
> > 
> > }
> > 
> > [OTG driver]
> > 
> > static int foo_otg_probe(pdev)
> > {
> > 
> > 	struct phy *phy;
> > 	/* ... */
> > 	phy = phy_get(&pdev->dev, "otgphy");
> > 	/* ... */
> > 
> > }
> 
> That's not so bad, as long as you let the phy core use whatever name it
> wants for the device when it registers it with sysfs.

Yes, in regulator core consumer names are completely separated from this. 
Regulator core simply assigns a sequential integer ID to each regulator 
and registers /sys/class/regulator/regulator.ID for each regulator.

> Use the name you
> are requesting as a "tag" or some such "hint" as to what the phy can be
> looked up by.
> 
> Good luck handling duplicate "tags" :)

The tag alone is not a key. Lookup key consists of two components, 
consumer device name and consumer tag. What kind of duplicate tags can be 
a problem here?

Best regards,
Tomasz

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