arch/x86/cpu_common: Add cpu_get_c_substate_support

Add a function to get the number of substates supported by
an Intel CPU C-state.

Test: Can read out the supported C-state substates.

Change-Id: Ie57e87609ea5d6ec6f37154e8b84f1e9574aa4a9
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78224
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/arch/x86/cpu_common.c

@@ -187,6 +187,22 @@ size_t get_cache_size(const struct cpu_cache_info *info)
 	return info->num_ways * info->physical_partitions * info->line_size * info->num_sets;
 }
 
+/*
+ * Returns the sub-states supported by the specified CPU
+ * C-state level.
+ *
+ * Level 0 corresponds to the lowest C-state (C0).
+ * Higher levels are processor specific.
+ */
+uint8_t cpu_get_c_substate_support(const int state)
+{
+	if ((cpuid_get_max_func() < 5) ||
+	    !(cpuid_ecx(5) & CPUID_FEATURE_MONITOR_MWAIT) || (state > 4))
+		return 0;
+
+	return (cpuid_edx(5) >> (state * 4)) & 0xf;
+}
+
 bool fill_cpu_cache_info(uint8_t level, struct cpu_cache_info *info)
 {
 	if (!info)

src/arch/x86/include/arch/cpu.h

@@ -99,6 +99,10 @@ static inline unsigned int cpuid_get_max_func(void)
 #define CPUID_CACHE_NO_OF_SETS_MASK 0xffffffff
 #define CPUID_CACHE_NO_OF_SETS(res) CPUID_CACHE(NO_OF_SETS, (res).ecx)
 
+// Intel leaf 0x5
+#define CPUID_FEATURE_MONITOR_MWAIT		(1 << 0)
+#define CPUID_FEATURE_INTERUPT_BREAK_EVENT	(1 << 1)
+
 unsigned int cpu_cpuid_extended_level(void);
 int cpu_have_cpuid(void);
 
@@ -310,6 +314,15 @@ size_t cpu_get_max_cache_share(const struct cpu_cache_info *info);
 /* get_cache_size to calculate the cache size. */
 size_t get_cache_size(const struct cpu_cache_info *info);
 
+/*
+ * Returns the sub-states supported by the specified CPU
+ * C-state level.
+ *
+ * Level 0 corresponds to the lowest C-state (C0).
+ * Higher levels are processor specific.
+ */
+uint8_t cpu_get_c_substate_support(const int state);
+
 /*
  * fill_cpu_cache_info to get all required cache info data and fill into cpu_cache_info
  * structure by calling CPUID.EAX=leaf and ECX=Cache Level.