x86/tsc: Remove CPUID "frequency" leaf magic numbers.

All the code that reads the CPUID frequency information leaf hard-codes
a magic number.  Give it a symbolic name and use it.

Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Zhao Liu <[email protected]>
Link: https://lore.kernel.org/all/20241213205036.4397658F%40davehans-spike.ostc.intel.com

Author: hansendc

arch/x86/include/asm/cpuid.h

@@ -24,6 +24,7 @@ enum cpuid_regs_idx {
 #define CPUID_MWAIT_LEAF	0x5
 #define CPUID_DCA_LEAF		0x9
 #define CPUID_TSC_LEAF		0x15
+#define CPUID_FREQ_LEAF		0x16
 
 #ifdef CONFIG_X86_32
 bool have_cpuid_p(void);

arch/x86/kernel/tsc.c

@@ -681,8 +681,8 @@ unsigned long native_calibrate_tsc(void)
 
 	/*
 	 * Denverton SoCs don't report crystal clock, and also don't support
-	 * CPUID.0x16 for the calculation below, so hardcode the 25MHz crystal
-	 * clock.
+	 * CPUID_FREQ_LEAF for the calculation below, so hardcode the 25MHz
+	 * crystal clock.
 	 */
 	if (crystal_khz == 0 &&
 			boot_cpu_data.x86_vfm == INTEL_ATOM_GOLDMONT_D)
@@ -701,10 +701,10 @@ unsigned long native_calibrate_tsc(void)
 	 * clock, but we can easily calculate it to a high degree of accuracy
 	 * by considering the crystal ratio and the CPU speed.
 	 */
-	if (crystal_khz == 0 && boot_cpu_data.cpuid_level >= 0x16) {
+	if (crystal_khz == 0 && boot_cpu_data.cpuid_level >= CPUID_FREQ_LEAF) {
 		unsigned int eax_base_mhz, ebx, ecx, edx;
 
-		cpuid(0x16, &eax_base_mhz, &ebx, &ecx, &edx);
+		cpuid(CPUID_FREQ_LEAF, &eax_base_mhz, &ebx, &ecx, &edx);
 		crystal_khz = eax_base_mhz * 1000 *
 			eax_denominator / ebx_numerator;
 	}
@@ -739,12 +739,12 @@ static unsigned long cpu_khz_from_cpuid(void)
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
-	if (boot_cpu_data.cpuid_level < 0x16)
+	if (boot_cpu_data.cpuid_level < CPUID_FREQ_LEAF)
 		return 0;
 
 	eax_base_mhz = ebx_max_mhz = ecx_bus_mhz = edx = 0;
 
-	cpuid(0x16, &eax_base_mhz, &ebx_max_mhz, &ecx_bus_mhz, &edx);
+	cpuid(CPUID_FREQ_LEAF, &eax_base_mhz, &ebx_max_mhz, &ecx_bus_mhz, &edx);
 
 	return eax_base_mhz * 1000;
 }