linux-kernel - Re: [PATCH] cpufreq: ARM big LITTLE: Add generic cpufreq driver and its DT glue

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Date:	Thu, 7 Mar 2013 10:03:28 +0800
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	rjw@...k.pl, Steve.Bannister@....com, linux-pm@...r.kernel.org,
	Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>,
	Liviu.Dudau@....com, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, robin.randhawa@....com,
	linux-arm-kernel@...ts.infradead.org, mark.hambleton@...adcom.com,
	linaro-kernel@...ts.linaro.org, charles.garcia-tobin@....com
Subject: Re: [PATCH] cpufreq: ARM big LITTLE: Add generic cpufreq driver and
 its DT glue

On 7 March 2013 08:51, Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> On Thu, Mar 07, 2013 at 08:32:37AM +0800, Viresh Kumar wrote:
>> On 5 March 2013 18:52, Russell King - ARM Linux <linux@....linux.org.uk> wrote:
>> > On Tue, Mar 05, 2013 at 12:52:41PM +0800, Viresh Kumar wrote:
>> >> +     clk[cluster] = clk_get(NULL, name);
>> >> +     if (!IS_ERR_OR_NULL(clk[cluster])) {
>> >
>> > NAK.  Two reasons.
>> >
>> > 1. IS_ERR_OR_NULL.  You know about this, it's been on the list several
>> >    times.
>>
>> Hey, i had a second thought about this one and i have some other opinion
>> here. This is a cpufreq driver and we need clock support for sure here, we
>> can't work without it. And so here is the latest fixup:
>
> NAK.  You just don't understand.

Poor me!!

I still remember the huge discussions we had during "clk: Add non
CONFIG_HAVE_CLK routines" patchset.

For others: https://lkml.org/lkml/2012/4/24/389

Back to the discussion, I understand that clk_get() just returns a cookie and
NULL is not an error and so it shouldn't be treated specially. And that's what
we do with most of our drivers as all other clk routines (clk_get[set]_rate())
have safe guards against the NULL clk, and they wouldn't complain.

The special case we have in a cpufreq driver is, we can't work with
zero returned
from clk_get_rate()... That will make cpufreq driver work badly.

And that's why i got two additions
- depends on HAVE_CLK
- and using IS_ERR_OR_NULL

as NULL returned from clk_get is not a error but is not acceptable to
the cpufreq
driver.

Because i now have the HAVE_CLK dependency i am not sure if we can get NULL
returned from clk_get() at all. Can you get around something here?

--
viresh
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