[RFC PATCH 3/3] CPPC: add support for SW BOOST

[Xiongfeng Wang]

To add SW BOOST support for CPPC, we need to get the max frequency of
boost mode and non-boost mode. ACPI spec 6.2 section 8.4.7.1 describe
the following two CPC registers.

"Highest performance is the absolute maximum performance an individual
processor may reach, assuming ideal conditions. This performance level
may not be sustainable for long durations, and may only be achievable if
other platform components are in a specific state; for example, it may
require other processors be in an idle state.

Nominal Performance is the maximum sustained performance level of the
processor, assuming ideal operating conditions. In absence of an
external constraint (power, thermal, etc.) this is the performance level
the platform is expected to be able to maintain continuously. All
processors are expected to be able to sustain their nominal performance
state simultaneously."

To add SW BOOST support for CPPC, we can use Highest Performance as the
max performance in boost mode and Nominal Performance as the max
performance in non-boost mode. If the Highest Performance is greater
than the Nominal Performance, we assume SW BOOST is supported.

The current CPPC driver does not support SW BOOST and use 'Highest
Performance' as the max performance the CPU can achieve. 'Nominal
Performance' is used to convert 'performance' to 'frequency'. That
means, if firmware enable boost and provide a value for Highest
Performance which is greater than Nominal Performance, boost feature is
enabled by default.

Because SW BOOST is disabled by default, so, after this patch, boost
feature is disabled by default even if boost is enabled by firmware.

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
---
 drivers/cpufreq/cppc_cpufreq.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index bda0b24..6ae070f 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -310,7 +310,7 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	 * Section 8.4.7.1.1.5 of ACPI 6.1 spec)
 	 */
 	policy->min = cppc_cpufreq_perf_to_khz(cpu, cpu->perf_caps.lowest_nonlinear_perf);
-	policy->max = cppc_cpufreq_perf_to_khz(cpu, cpu->perf_caps.highest_perf);
+	policy->max = cppc_cpufreq_perf_to_khz(cpu, cpu->perf_caps.nominal_perf);
 
 	/*
 	 * Set cpuinfo.min_freq to Lowest to make the full range of performance
@@ -318,7 +318,7 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	 * nonlinear perf
 	 */
 	policy->cpuinfo.min_freq = cppc_cpufreq_perf_to_khz(cpu, cpu->perf_caps.lowest_perf);
-	policy->cpuinfo.max_freq = cppc_cpufreq_perf_to_khz(cpu, cpu->perf_caps.highest_perf);
+	policy->cpuinfo.max_freq = cppc_cpufreq_perf_to_khz(cpu, cpu->perf_caps.nominal_perf);
 
 	policy->transition_delay_us = cppc_cpufreq_get_transition_delay_us(cpu_num);
 	policy->shared_type = cpu->shared_type;
@@ -343,6 +343,19 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
 	cpu->cur_policy = policy;
 
+	/*
+	 * If 'highest_perf' is greater than 'nominal_perf', we assume CPU Boost
+	 * is supported.
+	 */
+	if (cpu->perf_caps.highest_perf > cpu->perf_caps.nominal_perf) {
+		policy->cpuinfo.boost_max_freq = cppc_cpufreq_perf_to_khz(cpu,
+						cpu->perf_caps.highest_perf);
+		policy->cpuinfo.nonboost_max_freq = cppc_cpufreq_perf_to_khz(cpu,
+						cpu->perf_caps.nominal_perf);
+
+		cpufreq_enable_boost_support();
+	}
+
 	/* Set policy->cur to max now. The governors will adjust later. */
 	policy->cur = cppc_cpufreq_perf_to_khz(cpu,
 					cpu->perf_caps.highest_perf);
-- 
1.7.12.4