Re: [PATCH 2/2] cpufreq, intel_pstate, fix limits->max_perf rounding error

["Pandruvada, Srinivas" <srinivas.pandruvada@intel.com>]

On Fri, 2015-11-20 at 18:47 -0500, Prarit Bhargava wrote:
> A rounding error was found in the calculation of limits->max_perf
> in intel_pstate_set_policy(), which is used to calculate the max and min
> pstate values in intel_pstate_get_min_max().  In that code,
> limits->max_perf is truncated to 2 hex digits such that, for example,
> 0x169 was incorrectly calculated to 0x16 instead of 0x17.  This resulted in
> the pstate being set one level too low.  This patch rounds the value of
> limits->max_perf up instead of down so that the correct max pstate can
> be reached.
> 
> Cc: Srinivas Pandruvada <srinivas.pandruvada@intel.com>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Alexandra Yates <alexandra.yates@intel.com>
> Cc: Kristen Carlson Accardi <kristen@linux.intel.com>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: linux-pm@vger.kernel.org
> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index eb75053..8ad1f95 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1121,6 +1121,7 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>  				   limits->max_sysfs_pct);
>  	limits->max_perf_pct = max(limits->min_policy_pct,
>  				   limits->max_perf_pct);
> +	limits->max_perf = round_up(limits->max_perf, 8);
>  
>  	/* Make sure min_perf_pct <= max_perf_pct */
>  	limits->min_perf_pct = min(limits->max_perf_pct, limits->min_perf_pct);