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

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Date:	Tue, 13 Aug 2013 16:14:44 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	<balbi@...com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	<kyungmin.park@...sung.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 Wednesday 31 July 2013 11:45 AM, Felipe Balbi wrote:
> Hi,
> 
> On Wed, Jul 31, 2013 at 11:14:32AM +0530, Kishon Vijay Abraham I wrote:
>>>>>>> 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.
>>>>
>>>> And I'm saying that this idea, of using a specific name and id, is
>>>> frought with fragility and will break in the future in various ways when
>>>> devices get added to systems, making these strings constantly have to be
>>>> kept up to date with different board configurations.
>>>>
>>>> People, NEVER, hardcode something like an id.  The fact that this
>>>> happens today with the clock code, doesn't make it right, it makes the
>>>> clock code wrong.  Others have already said that this is wrong there as
>>>> well, as systems change and dynamic ids get used more and more.
>>>>
>>>> Let's not repeat the same mistakes of the past just because we refuse to
>>>> learn from them...
>>>>
>>>> So again, the "find a phy by a string" functions should be removed, the
>>>> device id should be automatically created by the phy core just to make
>>>> things unique in sysfs, and no driver code should _ever_ be reliant on
>>>> the number that is being created, and the pointer to the phy structure
>>>> should be used everywhere instead.
>>>>
>>>> With those types of changes, I will consider merging this subsystem, but
>>>> without them, sorry, I will not.
>>>
>>> I'll agree with Greg here, the very fact that we see people trying to
>>> add a requirement of *NOT* using PLATFORM_DEVID_AUTO already points to a
>>> big problem in the framework.
>>>
>>> The fact is that if we don't allow PLATFORM_DEVID_AUTO we will end up
>>> adding similar infrastructure to the driver themselves to make sure we
>>> don't end up with duplicate names in sysfs in case we have multiple
>>> instances of the same IP in the SoC (or several of the same PCIe card).
>>> I really don't want to go back to that.
>>
>> If we are using PLATFORM_DEVID_AUTO, then I dont see any way we can give the
>> correct binding information to the PHY framework. I think we can drop having
>> this non-dt support in PHY framework? I see only one platform (OMAP3) going to
>> be needing this non-dt support and we can use the USB PHY library for it.
> 
> you shouldn't drop support for non-DT platform, in any case we lived
> without DT (and still do) for years. Gotta find a better way ;-)

hmm..

how about passing the device names of PHY in platform data of the controller?
It should be deterministic as the PHY framework assigns its own id and we
*don't* want to add any requirement that the ID must be assigned manually
without using PLATFORM_DEVID_AUTO. We can get rid of *phy_init_data* in the v10
patch series.

Thanks
Kishon
> 

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