linux-kernel - [PATCH 07/10] x86/tsc: Remove CPUID "frequency" leaf magic numbers.

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Message-Id: <20241213205036.4397658F@davehans-spike.ostc.intel.com>
Date: Fri, 13 Dec 2024 12:50:36 -0800
From: Dave Hansen <dave.hansen@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,tglx@...utronix.de,bp@...en8.de,rafael@...nel.org,lenb@...nel.org,dave.jiang@...el.com,irenic.rajneesh@...il.com,david.e.box@...el.com,Dave Hansen <dave.hansen@...ux.intel.com>,zhao1.liu@...el.com
Subject: [PATCH 07/10] x86/tsc: Remove CPUID "frequency" leaf magic numbers.


From: Dave Hansen <dave.hansen@...ux.intel.com>

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 <dave.hansen@...ux.intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@...el.com>
---

 b/arch/x86/include/asm/cpuid.h |    1 +
 b/arch/x86/kernel/tsc.c        |   12 ++++++------
 2 files changed, 7 insertions(+), 6 deletions(-)

diff -puN arch/x86/include/asm/cpuid.h~tsc-leaf-checks-3 arch/x86/include/asm/cpuid.h
--- a/arch/x86/include/asm/cpuid.h~tsc-leaf-checks-3	2024-12-13 12:45:35.839181468 -0800
+++ b/arch/x86/include/asm/cpuid.h	2024-12-13 12:45:35.843181638 -0800
@@ -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);
diff -puN arch/x86/kernel/tsc.c~tsc-leaf-checks-3 arch/x86/kernel/tsc.c
--- a/arch/x86/kernel/tsc.c~tsc-leaf-checks-3	2024-12-13 12:45:35.839181468 -0800
+++ b/arch/x86/kernel/tsc.c	2024-12-13 12:45:35.843181638 -0800
@@ -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(
 	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;
 }
_