linux-kernel - Re: [PATCH v3 0/5] common clk framework

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Date:	Tue, 22 Nov 2011 10:09:29 -0800
From:	Mike Turquette <mturquette@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Greg KH <greg@...ah.com>, Mike Turquette <mturquette@...com>,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, jeremy.kerr@...onical.com,
	broonie@...nsource.wolfsonmicro.com, tglx@...utronix.de,
	linus.walleij@...ricsson.com, amit.kucheria@...aro.org,
	dsaxena@...aro.org, patches@...aro.org,
	linaro-dev@...ts.linaro.org, paul@...an.com,
	grant.likely@...retlab.ca, sboyd@...cinc.com,
	shawn.guo@...escale.com, skannan@...cinc.com,
	magnus.damm@...il.com, arnd.bergmann@...aro.org,
	eric.miao@...aro.org, richard.zhao@...aro.org
Subject: Re: [PATCH v3 0/5] common clk framework

On Tue, Nov 22, 2011 at 9:45 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Tue, Nov 22, 2011 at 07:42:59AM -0800, Greg KH wrote:
>> On Mon, Nov 21, 2011 at 05:40:42PM -0800, Mike Turquette wrote:
>> >   .sysfs support.  Visualize your clk tree at /sys/clk!  Where would be
>> > a better place to put the clk tree besides the root of /sys/?
>>
>> Um, in the "proper" place for it under /sys/devices like the rest of the
>> device tree is?
>
> I'd suggest that making the clock tree visible in sysfs (and therefore
> part of the kernel ABI) is not a good idea.  Some of the nodes in there
> will be specific to the implementation.  Exposing the clock nodes means
> that if you have to change the clock tree structure, you change the
> visible userspace ABI.

It is true that the ABI will change dynamically.

>
> So, I'd suggest that we need to see a justification for this, rather
> than exposing this stuff via debugfs as has been done with existing
> implementations.

Userspace tools like powerdebug (and maybe someday powertop) hope to
use a reliable-looking interface to view clk data.  There are obvious
uses for this data in a debug tool, the most obvious of which is
"which clk isn't turning off when it should?".

I can migrate this stuff to debugfs, but it adds the burden of having
debugfs enabled for folks that want to view this data.  I would also
argue that sysfs is there to model various aspects of system topology
and a clk tree certainly fits the bill.

If others also agree that it should reside only in debugfs then I'll
move it there for V4.

Thanks,
Mike
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