[PATCH v2] cpufreq: acpi-cpufreq: use DMI max speed when CPPC is unavailable

[Henry Tseng <henrytseng@qnap.com>]

On AMD Ryzen Embedded V1780B (Family 17h, Zen 1), the BIOS does not
provide ACPI _CPC objects and the CPU does not support MSR-based CPPC
(X86_FEATURE_CPPC).  The _PSS table only lists nominal P-states
(P0 = 3350 MHz), so when get_max_boost_ratio() fails at
cppc_get_perf_caps(), cpuinfo_max_freq reports only the base frequency
instead of the rated boost frequency (3600 MHz).

  dmesg:
    ACPI CPPC: No CPC descriptor for CPU:0
    acpi_cpufreq: CPU0: Unable to get performance capabilities (-19)

cppc-cpufreq already has a DMI fallback (cppc_get_dmi_max_khz()) that
reads the processor max speed from SMBIOS Type 4.  Export it and reuse
it in acpi-cpufreq as a last-resort source for the boost frequency.

A sanity check ensures the DMI value is above the _PSS P0 frequency
and within 2x of it; values outside that range are ignored and the
existing arch_set_max_freq_ratio() path is taken instead.  The 2x
upper bound is based on a survey of the AMD Ryzen Embedded V1000
series, where the highest boost-to-base ratio is 1.8x (V1404I:
2.0 GHz base / 3.6 GHz boost).

The DMI lookup and sanity check are wrapped in a helper,
acpi_cpufreq_resolve_max_freq(), which falls through to
arch_set_max_freq_ratio() if the DMI value is absent or
out of range.

Tested on AMD Ryzen Embedded V1780B with v7.0-rc4:

  Before: cpuinfo_max_freq = 3350000 (base only)
  After:  cpuinfo_max_freq = 3600000 (includes boost)

Link: https://www.amd.com/en/products/embedded/ryzen/ryzen-v1000-series.html#specifications
Signed-off-by: Henry Tseng <henrytseng@qnap.com>
---
v2:
  - Extract else block into acpi_cpufreq_resolve_max_freq()
    to avoid #ifdef in the main init path (Rafael)
v1:
  - https://lore.kernel.org/linux-pm/20260320095648.3598007-1-henrytseng@qnap.com/

 drivers/acpi/cppc_acpi.c       |  3 ++-
 drivers/cpufreq/acpi-cpufreq.c | 31 ++++++++++++++++++++++++-------
 include/acpi/cppc_acpi.h       |  1 +
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index f0e513e9ed5d..f53de414acf2 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1944,7 +1944,7 @@ static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private)
 }
 
 /* Look up the max frequency in DMI */
-static u64 cppc_get_dmi_max_khz(void)
+u64 cppc_get_dmi_max_khz(void)
 {
 	u16 mhz = 0;
 
@@ -1958,6 +1958,7 @@ static u64 cppc_get_dmi_max_khz(void)
 
 	return KHZ_PER_MHZ * mhz;
 }
+EXPORT_SYMBOL_GPL(cppc_get_dmi_max_khz);
 
 /*
  * If CPPC lowest_freq and nominal_freq registers are exposed then we can
diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index e7eff6c2f092..21639d9ac753 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -675,6 +675,29 @@ static inline u64 get_max_boost_ratio(unsigned int cpu, u64 *nominal_freq)
 }
 #endif
 
+static void acpi_cpufreq_resolve_max_freq(struct cpufreq_policy *policy,
+					  unsigned int pss_max_freq)
+{
+#ifdef CONFIG_ACPI_CPPC_LIB
+	u64 max_speed = cppc_get_dmi_max_khz();
+	/*
+	 * Use DMI "Max Speed" if it looks plausible: must be
+	 * above _PSS P0 frequency and within 2x of it.
+	 */
+	if (max_speed > pss_max_freq && max_speed < pss_max_freq * 2) {
+		policy->cpuinfo.max_freq = max_speed;
+		return;
+	}
+#endif
+	/*
+	 * If the maximum "boost" frequency is unknown, ask the arch
+	 * scale-invariance code to use the "nominal" performance for
+	 * CPU utilization scaling so as to prevent the schedutil
+	 * governor from selecting inadequate CPU frequencies.
+	 */
+	arch_set_max_freq_ratio(true);
+}
+
 static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
 {
 	struct cpufreq_frequency_table *freq_table;
@@ -849,13 +872,7 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
 		policy->cpuinfo.max_freq = freq * max_boost_ratio >> SCHED_CAPACITY_SHIFT;
 	} else {
-		/*
-		 * If the maximum "boost" frequency is unknown, ask the arch
-		 * scale-invariance code to use the "nominal" performance for
-		 * CPU utilization scaling so as to prevent the schedutil
-		 * governor from selecting inadequate CPU frequencies.
-		 */
-		arch_set_max_freq_ratio(true);
+		acpi_cpufreq_resolve_max_freq(policy, freq_table[0].frequency);
 	}
 
 	policy->freq_table = freq_table;
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 4d644f03098e..e6c5ef3173c5 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -156,6 +156,7 @@ extern int cppc_set_enable(int cpu, bool enable);
 extern int cppc_get_perf_caps(int cpu, struct cppc_perf_caps *caps);
 extern bool cppc_perf_ctrs_in_pcc_cpu(unsigned int cpu);
 extern bool cppc_perf_ctrs_in_pcc(void);
+extern u64 cppc_get_dmi_max_khz(void);
 extern unsigned int cppc_perf_to_khz(struct cppc_perf_caps *caps, unsigned int perf);
 extern unsigned int cppc_khz_to_perf(struct cppc_perf_caps *caps, unsigned int freq);
 extern bool acpi_cpc_valid(void);
-- 
2.43.0