Re: [PATCH] cpufreq: arm_big_little: fix frequency check when bL switcher is active

From: Sudeep Holla <sudeep.holla@arm.com>
To: "Jon Medhurst (Tixy)" <tixy@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cpufreq: arm_big_little: fix frequency check when bL switcher is active
Date: Wed, 14 Oct 2015 09:48:32 +0100	[thread overview]
Message-ID: <561E16E0.8030906@arm.com> (raw)
In-Reply-To: <1444806720.2691.15.camel@linaro.org>

On 14/10/15 08:12, Jon Medhurst (Tixy) wrote:
> On Tue, 2015-10-13 at 11:36 +0100, Sudeep Holla wrote:
>>
>> On 13/10/15 08:19, Jon Medhurst (Tixy) wrote:
> [...]
>>> But then we wouldn't get the WARN_ON and pr_err triggered when we detect
>>> the clock rate isn't set, which surely is half the reason for the check
>>> in the first place?
>>>
>>
>> Not sure if I understand what you mean or may be I was not clear, so
>> thought I will put the delta here. Let me know if and how its still a
>> problem.
>>
>> diff --git i/drivers/cpufreq/arm_big_little.c
>> w/drivers/cpufreq/arm_big_little.c
>> index f1e42f8ce0fc..05e850f80f39 100644
>> --- i/drivers/cpufreq/arm_big_little.c
>> +++ w/drivers/cpufreq/arm_big_little.c
>> @@ -164,6 +164,16 @@ bL_cpufreq_set_rate(u32 cpu, u32 old_cluster, u32
>> new_cluster, u32 rate)
>>
>>           mutex_unlock(&cluster_lock[new_cluster]);
>>
>> +       /*
>> +        * FIXME: clk_set_rate has to handle the case where clk_change_rate
>> +        * can fail due to hardware or firmware issues. Until the clk core
>> +        * layer is fixed, we can check here. In most of the cases we will
>> +        * be reading only the cached value anyway. This needs to  be
>> removed
>> +        * once clk core is fixed.
>> +        */
>> +       if (bL_cpufreq_get_rate(cpu) != new_rate)
>> +               return -EIO;
>> +
>>           /* Recalc freq for old cluster when switching clusters */
>>           if (old_cluster != new_cluster) {
>>                   pr_debug("%s: cpu: %d, old cluster: %d, new cluster: %d\n",
>
> That's what I though you meant, and I can't see why you would want to do
> that and bypass the error reporting for clk_get_rate failing. After all,
> the code we're moving around is explicitly there to workaround the fact
> that clk_set_rate doesn't actually pass through all errors, so it's
> doing additional error checking. (At least, that's what the comment
> says). So this looks more logical to me.
>

OK, I understand what you mean now. I don't have a strong opinion, but
here is the reason why I prefer the approach I said earlier:
clk_set_rate doesn't return error if the h/w or f/w return error which
is usually the last step. So calling clk_get_rate when clk_set_rate
return error quite early makes no sense to me.

-- 
Regards,
Sudeep