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 21:00:35 -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 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.
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