linux-kernel - Re: [PATCH v2] cpufreq: arm_big_little: fix frequency check when bL switcher is active

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Message-ID: <20151021095725.GA7784@ubuntu>
Date:	Wed, 21 Oct 2015 15:27:25 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
Cc:	Sudeep Holla <sudeep.holla@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH v2] cpufreq: arm_big_little: fix frequency check when bL
 switcher is active

On 21-10-15, 10:55, Jon Medhurst (Tixy) wrote:
> The check for correct frequency being set in bL_cpufreq_set_rate is
> broken when the big.LITTLE switcher is active, for two reasons.
> 
> 1. The 'new_rate' variable gets overwritten before the test by the
> code calculating the frequency of the old cluster.
> 
> 2. The frequency returned by bL_cpufreq_get_rate will be the virtual
> frequency, not the actual one the intended version of new_rate contains.
> 
> This means the function always returns an error causing an endless
> stream of: "cpufreq: __target_index: Failed to change cpu frequency: -5"
> 
> As the intent is to check for errors that clk_set_rate doesn't report
> lets move the check to immediately after that and directly use
> clk_get_rate, rather than the arm_big_little helpers which only confuse
> matters. Also, update the comment to be hopefully clearer about the
> purpose of the code.
> 
> Fixes: 0a95e630b49a ("cpufreq: arm_big_little: check if the frequency is set correctly")
> 
> Signed-off-by: Jon Medhurst <tixy@...aro.org>
> Acked-by: Sudeep Holla <sudeep.holla@....com>
> ---
> 
> Changes since V1:
> - Check rate using clk_get_rate rather than disabling check when bL
>   switcher active
> 
> Sudeep, I added your Ack from the last comment on the previous patch.
> This final patch differs from what was discussed only in the commit
> message and in source comment which is hopefully more clear and is
> also satisfactory.
> 
> I've also added Michael Turquette's correct email to the CC this time,
> rather than his old Linaro address which was bouncing.
> 
>  drivers/cpufreq/arm_big_little.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
> 

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh
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