[PATCH v10 6/8] cpufreq: amd-pstate: get transition delay and latency value from ACPI tables

Perry Yuan
2024-03-25T03:04:27Z

Make pstate driver initially retrieve the P-state transition delay and
latency values from the BIOS ACPI tables which has more reasonable
delay and latency values according to the platform design and
requirements.

Previously there values were hardcoded at specific value which may
have conflicted with platform and it might not reflect the most
accurate or optimized setting for the processor.

[054h 0084 8] Preserve Mask : FFFFFFFF00000000
[05Ch 0092 8] Write Mask : 0000000000000001
[064h 0100 4] Command Latency : 00000FA0
[068h 0104 4] Maximum Access Rate : 0000EA60
[06Ch 0108 2] Minimum Turnaround Time : 0000

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Tested-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>
Signed-off-by: Perry Yuan <perry.yuan@amd.com>
---
drivers/cpufreq/amd-pstate.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 6708c436e1a2..ec049b62b366 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -756,6 +756,36 @@ static void amd_pstate_update_limits(unsigned int cpu)
mutex_unlock(&amd_pstate_driver_lock);
}

+/**
+ * Get pstate transition delay time from ACPI tables that firmware set
+ * instead of using hardcode value directly.
+ */
+static u32 amd_pstate_get_transition_delay_us(unsigned int cpu)
+{
+ u32 transition_delay_ns;
+
+ transition_delay_ns = cppc_get_transition_latency(cpu);
+ if (transition_delay_ns == CPUFREQ_ETERNAL)
+ return AMD_PSTATE_TRANSITION_DELAY;
+
+ return transition_delay_ns / NSEC_PER_USEC;
+}
+
+/**
+ * Get pstate transition latency value from ACPI tables that firmware
+ * set instead of using hardcode value directly.
+ */
+static u32 amd_pstate_get_transition_latency(unsigned int cpu)
+{
+ u32 transition_latency;
+
+ transition_latency = cppc_get_transition_latency(cpu);
+ if (transition_latency == CPUFREQ_ETERNAL)
+ return AMD_PSTATE_TRANSITION_LATENCY;
+
+ return transition_latency;
+}
+
/**
* amd_pstate_init_freq: Initialize the max_freq, min_freq,
* nominal_freq and lowest_nonlinear_freq for
@@ -848,8 +878,8 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
goto free_cpudata1;
}

- policy->cpuinfo.transition_latency = AMD_PSTATE_TRANSITION_LATENCY;
- policy->transition_delay_us = AMD_PSTATE_TRANSITION_DELAY;
+ policy->cpuinfo.transition_latency = amd_pstate_get_transition_latency(policy->cpu);
+ policy->transition_delay_us = amd_pstate_get_transition_delay_us(policy->cpu);

policy->min = min_freq;
policy->max = max_freq;
--
2.34.1