Message-ID: <520B9C9E.8010002@ti.com>
Date:	Wed, 14 Aug 2013 20:35:02 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Tomasz Figa <tomasz.figa@...il.com>, <balbi@...com>
CC:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Tomasz Figa <t.figa@...sung.com>,
	<linux-fbdev@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<tony@...mide.com>, <nsekhar@...com>, <s.nawrocki@...sung.com>,
	<kgene.kim@...sung.com>, <swarren@...dia.com>,
	<jg1.han@...sung.com>, Alan Stern <stern@...land.harvard.edu>,
	<grant.likely@...aro.org>, <linux-media@...r.kernel.org>,
	<george.cherian@...com>, <arnd@...db.de>,
	<devicetree-discuss@...ts.ozlabs.org>,
	<linux-samsung-soc@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <balajitk@...com>,
	Greg KH <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kyungmin.park@...sung.com>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH 01/15] drivers: phy: add generic PHY framework

Hi,

On Wednesday 14 August 2013 04:34 AM, Tomasz Figa wrote:
> On Wednesday 14 of August 2013 00:19:28 Sylwester Nawrocki wrote:
>> W dniu 2013-08-13 14:05, Kishon Vijay Abraham I pisze:
>>> On Tuesday 13 August 2013 05:07 PM, Tomasz Figa wrote:
>>>> On Tuesday 13 of August 2013 16:14:44 Kishon Vijay Abraham I wrote:
>>>>> On Wednesday 31 July 2013 11:45 AM, Felipe Balbi wrote:
>>>>>> 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.
>>
>> OK, so the PHY device name would have a fixed part, passed as
>> platform data of the controller and a variable part appended
>> by the PHY core, depending on the number of registered PHYs ?
>>
>> Then same PHY names would be passed as the PHY provider driver's
>> platform data ?
>>
>> Then if there are 2 instances of the above (same names in platform
>> data) how would be determined which PHY controller is linked to
>> which PHY supplier ?
>>
>> I guess you want each device instance to have different PHY device
>> names already in platform data ? That might work. We probably will
>> be focused mostly on DT anyway. It seem without DT we are trying
>> to find some layer that would allow us to couple relevant devices
>> and overcome driver core inconvenience that it provides to means
>> to identify specific devices in advance. :) Your proposal sounds
>> reasonable, however I might be missing some details or corner cases.
>>
>>>> What about slightly altering the concept of v9 to pass a pointer to
>>>> struct device instead of device name inside phy_init_data?
>>
>> As Felipe said, we don't want to pass pointers in platform_data
>> to/from random subsystems. We pass data, passing pointers would
>> be a total mess IMHO.
> 
> Well, this is a total mess anyway... I don't really get the point of using 
> PLATFORM_DEVID_AUTO. The only thing that comes to my mind is that you can 
> use it if you don't care about the ID and so it can be assigned 
> automatically.
> 
> However my understanding of the device ID is that it was supposed to 
> provide a way to identify multiple instances of identical devices in a 
> reliable way, to solve problems like the one we are trying to solve 
> here...
> 
> So maybe let's stop solving an already solved problem and just state that 
> you need to explicitly assign device ID to use this framework?

Felipe,
Can we have it the way I had in my v10 patch series till we find a better way?
I think this *non-dt* stuff shouldn't be blocking as most of the users are dt only?

Thanks
Kishon
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