linux-kernel - Re: [PATCH] cpufreq: Make sure CPU is running on a freq from freq-table

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Message-ID: <528F01C4.1050608@linaro.org>
Date:	Fri, 22 Nov 2013 12:33:32 +0530
From:	viresh kumar <viresh.kumar@...aro.org>
To:	nm@...com
CC:	rjw@...ysocki.net, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	shawn.guo@...aro.org, ceh@...com,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH] cpufreq: Make sure CPU is running on a freq from freq-table

On Thursday 21 November 2013 12:39 PM, Viresh Kumar wrote:
> Sometimes boot loaders set CPU frequency to a value outside of frequency table
> present with cpufreq core. In such cases CPU might be unstable if it has to run
> on that frequency for long duration of time and so its better to set it to a
> frequency which is specified in freq-table. This also makes cpufreq stats
> inconsistent as cpufreq-stats would fail to register because current frequency
> of CPU isn't found in freq-table.
> 
> Because we don't want this change to effect boot process badly, we go for the
> next freq which is >= policy->cur ('cur' must be set by now, otherwise we will
> end up setting freq to lowest of the table as 'cur' is initialized to zero).
> 
> In case where CPU is already running on one of the frequencies present in
> freq-table, this would turn into a dummy call as __cpufreq_driver_target() would
> return early.
> 
> Reported-by: Carlos Hernandez <ceh@...com>
> Reported-by: Nishanth Menon <nm@...com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

Copying another mail from Nishant here to get my cc'list back..

On Friday 22 November 2013 05:12 AM, Nishanth Menon wrote:
> I gave this a quick run on my 3.12 kernel:
> http://pastebin.mozilla.org/3649730 is what I applied and output
> http://pastebin.mozilla.org/3649729
>
> I need to see what I might have mucked up.. or see if I can test this
> on 3.13 master on a different board (since OMAP5 wont boot in master
> without clock dts nodes :()..

This happened because of common sense, which was missing in my patch :)

Try this over existing patch:

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 6e8b226..e403388 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1126,13 +1126,19 @@ static int __cpufreq_add_dev(struct device *dev, struct
subsys_interface *sif,
         * In case where CPU is already running on one of the frequencies
         * present in freq-table, this would turn into a dummy call as
         * __cpufreq_driver_target() would return early.
+        *
+        * We are passing target-freq as "policy->cur - 1" otherwise
+        * __cpufreq_driver_target() would simply fail, as policy->cur will be
+        * equal to target-freq.
         */
        if (has_target()) {
-               ret = __cpufreq_driver_target(policy, policy->cur,
+               ret = __cpufreq_driver_target(policy, policy->cur - 1,
                                CPUFREQ_RELATION_L);
-               if (ret)
+               if (ret) {
                        pr_err("%s: Unable to set frequency from table: %d\n",
                                        __func__, ret);
+                       goto err_out_unregister;
+               }
        }

        /* related cpus should atleast have policy->cpus */

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