linux-kernel - Re: [PATCH v2 05/11] ARM: dt: tegra30: Add device node for APB MISC

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Date:	Thu, 03 Jan 2013 22:21:04 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Prashant Gaikwad <pgaikwad@...dia.com>
CC:	"mturquette@...aro.org" <mturquette@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v2 05/11] ARM: dt: tegra30: Add device node for APB MISC

On 01/03/2013 09:26 PM, Prashant Gaikwad wrote:
> On Friday 04 January 2013 09:30 AM, Stephen Warren wrote:
>> On 01/03/2013 08:23 PM, Prashant Gaikwad wrote:
>>> On Friday 04 January 2013 08:35 AM, Stephen Warren wrote:
>>>> On 01/03/2013 06:48 PM, Prashant Gaikwad wrote:
>>>>> On Thursday 03 January 2013 09:41 PM, Stephen Warren wrote:
>> ...
>>>>>> OK. It sounds like we need a true APB MISC driver then, to
>>>>>> abstract the
>>>>>> differences; the clock driver really shouldn't be touching the APB
>>>>>> MISC
>>>>>> registers in all likelihood, unless a subset of the sections you
>>>>>> mention
>>>>>> above are truly dedicated to clock functionality.
>>>>> I don't think it is a good idea to create a driver for APB MISC, all
>>>>> registers are used by different drivers.
>>>> Well, it's even worse to have a bunch of other drivers randomly trample
>>>> on a set of registers they don't own.
>>>>
>>>>> Only chip id revision registers are used in clock driver.
>>>> There are already global variables exposed by the Tegra fuse driver;
>>>> can
>>>> you just read those?
>>> It is not about variables or some value, we have to read some apb
>>> register to flush the write operation in apb bus before we disable
>>> peripheral clock.
>>> We are using chip id revision register for this purpose.
>> Ah. That's definitely not something the clock driver should be doing
>> directly. It's probably OK to add a custom Tegra-specific function to
>> some file in arch/arm/mach-tegra to implement this. Even better would be
>> a full bus driver for the APB bus, but that's probably too much bloat
>> for now.
> 
> tegra_init_fuse in arch/arm/mach-tegra/fuse.c is already reading chip id
> revision register, so I can implement one function to read this register
> in fuse.c, which will be used by clock driver and tegra_init_fuse.
> But then we need to add it to some header file in include/mach or
> include/linux, where? any suggestion?

Somewhere other than arch/arm/mach-tega/include/mach/ would be good, so
we don't have to move it later when we enable multi-platform zImage for
Tegra. Perhaps include/linux/tegra-soc.h? I guess we could move the
existing mach/powergate.h contents into that file later too.
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