2018-03-23 10:32:18

by George Cherian

Subject: [PATCH] cpufreq: cppc: Use transition_delay_us depending on the transition_latency

With commit e948bc8fbee0 ("cpufreq: Cap the default transition delay
value to 10 ms") the cpufreq was not honouring the delay passed via
ACPI (PCCT). Due to which on ARM based platforms using CPPC the cpufreq
governor tries to change the frequency of CPU faster than expeted.

This leads to continuous error messages like the following.
" ACPI CPPC: PCC check channel failed. Status=0 "

Earlier (without above commit) the default transition delay was
taken form the value passed from PCCT. Use the same value provided by PCCT
to set the transition_delay_us.

Fixes: e948bc8fbee0 (cpufreq: Cap the default transition delay value to 10 ms)
Signed-off-by: George Cherian <[email protected]>
---
drivers/cpufreq/cppc_cpufreq.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index a1c3025..dcb1cb9 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -20,6 +20,7 @@
#include <linux/cpu.h>
#include <linux/cpufreq.h>
#include <linux/dmi.h>
+#include <linux/time.h>
#include <linux/vmalloc.h>

#include <asm/unaligned.h>
@@ -162,6 +163,8 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
policy->cpuinfo.max_freq = cppc_dmi_max_khz;

policy->cpuinfo.transition_latency = cppc_get_transition_latency(cpu_num);
+ policy->transition_delay_us = cppc_get_transition_latency(cpu_num) /
+ NSEC_PER_USEC;
policy->shared_type = cpu->shared_type;

if (policy->shared_type == CPUFREQ_SHARED_TYPE_ANY)
--
1.8.3.1

2018-03-30 10:18:06

by Rafael J. Wysocki

Subject: Re: [PATCH] cpufreq: cppc: Use transition_delay_us depending on the transition_latency

On Friday, March 23, 2018 11:30:31 AM CEST George Cherian wrote:
> With commit e948bc8fbee0 ("cpufreq: Cap the default transition delay
> value to 10 ms") the cpufreq was not honouring the delay passed via
> ACPI (PCCT). Due to which on ARM based platforms using CPPC the cpufreq
> governor tries to change the frequency of CPU faster than expeted.
>
> This leads to continuous error messages like the following.
> " ACPI CPPC: PCC check channel failed. Status=0 "
>
> Earlier (without above commit) the default transition delay was
> taken form the value passed from PCCT. Use the same value provided by PCCT
> to set the transition_delay_us.
>
> Fixes: e948bc8fbee0 (cpufreq: Cap the default transition delay value to 10 ms)
> Signed-off-by: George Cherian <[email protected]>
> ---
> drivers/cpufreq/cppc_cpufreq.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index a1c3025..dcb1cb9 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -20,6 +20,7 @@
> #include <linux/cpu.h>
> #include <linux/cpufreq.h>
> #include <linux/dmi.h>
> +#include <linux/time.h>
> #include <linux/vmalloc.h>
>
> #include <asm/unaligned.h>
> @@ -162,6 +163,8 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
> policy->cpuinfo.max_freq = cppc_dmi_max_khz;
>
> policy->cpuinfo.transition_latency = cppc_get_transition_latency(cpu_num);
> + policy->transition_delay_us = cppc_get_transition_latency(cpu_num) /
> + NSEC_PER_USEC;
> policy->shared_type = cpu->shared_type;
>
> if (policy->shared_type == CPUFREQ_SHARED_TYPE_ANY)
>

Applied, thanks!