From ad38677df44b67e0f5b6c4d31e9c2734abde8ed9 Mon Sep 17 00:00:00 2001 From: Al Stone Date: Wed, 20 Jul 2016 15:10:04 -0600 Subject: [PATCH] cpufreq: CPPC: Force reporting values in KHz to fix user space interface When CPPC is being used by ACPI on arm64, user space tools such as cpupower report CPU frequency values from sysfs that are incorrect. What the driver was doing was reporting the values given by ACPI tables in whatever scale was used to provide them. However, the ACPI spec defines the CPPC values as unitless abstract numbers. Internal kernel structures such as struct perf_cap, in contrast, expect these values to be in KHz. When these struct values get reported via sysfs, the user space tools also assume they are in KHz, causing them to report incorrect values (for example, reporting a CPU frequency of 1MHz when it should be 1.8GHz). The downside is that this approach has some assumptions: (1) It relies on SMBIOS3 being used, *and* that the Max Frequency value for a processor is set to a non-zero value. (2) It assumes that all processors run at the same speed, or that the CPPC values have all been scaled to reflect relative speed. This patch retrieves the largest CPU Max Frequency from a type 4 DMI record that it can find. This may not be an issue, however, as a sampling of DMI data on x86 and arm64 indicates there is often only one such record regardless. Since CPPC is relatively new, it is unclear if the ACPI ASL will always be written to reflect any sort of relative performance of processors of differing speeds. (3) It assumes that performance and frequency both scale linearly. For arm64 servers, this may be sufficient, but it does rely on firmware values being set correctly. Hence, other approaches will be considered in the future. This has been tested on three arm64 servers, with and without DMI, with and without CPPC support. Signed-off-by: Al Stone Signed-off-by: Prashanth Prakash Signed-off-by: Rafael J. Wysocki --- drivers/cpufreq/cppc_cpufreq.c | 53 +++++++++++++++++++++++++++++++--- 1 file changed, 49 insertions(+), 4 deletions(-) diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index 8882b8e2ecd0..6debc189a9c9 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -19,10 +19,19 @@ #include #include #include +#include #include +#include + #include +/* Minimum struct length needed for the DMI processor entry we want */ +#define DMI_ENTRY_PROCESSOR_MIN_LENGTH 48 + +/* Offest in the DMI processor structure for the max frequency */ +#define DMI_PROCESSOR_MAX_SPEED 0x14 + /* * These structs contain information parsed from per CPU * ACPI _CPC structures. @@ -32,6 +41,39 @@ */ static struct cpudata **all_cpu_data; +/* Capture the max KHz from DMI */ +static u64 cppc_dmi_max_khz; + +/* Callback function used to retrieve the max frequency from DMI */ +static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private) +{ + const u8 *dmi_data = (const u8 *)dm; + u16 *mhz = (u16 *)private; + + if (dm->type == DMI_ENTRY_PROCESSOR && + dm->length >= DMI_ENTRY_PROCESSOR_MIN_LENGTH) { + u16 val = (u16)get_unaligned((const u16 *) + (dmi_data + DMI_PROCESSOR_MAX_SPEED)); + *mhz = val > *mhz ? val : *mhz; + } +} + +/* Look up the max frequency in DMI */ +static u64 cppc_get_dmi_max_khz(void) +{ + u16 mhz = 0; + + dmi_walk(cppc_find_dmi_mhz, &mhz); + + /* + * Real stupid fallback value, just in case there is no + * actual value set. + */ + mhz = mhz ? mhz : 1; + + return (1000 * mhz); +} + static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, unsigned int target_freq, unsigned int relation) @@ -42,7 +84,7 @@ static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, cpu = all_cpu_data[policy->cpu]; - cpu->perf_ctrls.desired_perf = target_freq; + cpu->perf_ctrls.desired_perf = target_freq * policy->max / cppc_dmi_max_khz; freqs.old = policy->cur; freqs.new = target_freq; @@ -94,8 +136,10 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy) return ret; } - policy->min = cpu->perf_caps.lowest_perf; - policy->max = cpu->perf_caps.highest_perf; + cppc_dmi_max_khz = cppc_get_dmi_max_khz(); + + policy->min = cpu->perf_caps.lowest_perf * cppc_dmi_max_khz / cpu->perf_caps.highest_perf; + policy->max = cppc_dmi_max_khz; policy->cpuinfo.min_freq = policy->min; policy->cpuinfo.max_freq = policy->max; policy->shared_type = cpu->shared_type; @@ -112,7 +156,8 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy) cpu->cur_policy = policy; /* Set policy->cur to max now. The governors will adjust later. */ - policy->cur = cpu->perf_ctrls.desired_perf = cpu->perf_caps.highest_perf; + policy->cur = cppc_dmi_max_khz; + cpu->perf_ctrls.desired_perf = cpu->perf_caps.highest_perf; ret = cppc_set_perf(cpu_num, &cpu->perf_ctrls); if (ret)