x86, tsc: Remove CPU frequency calibration on AMD

6b37f5a20c0e5c334c010a587058354215433e92 introduced the CPU frequency
calibration code for AMD CPUs whose TSCs didn't increment with the
core's P0 frequency. From F10h, revB onward, however, the TSC increment
rate is denoted by MSRC001_0015[24] and when this bit is set (which
should be done by the BIOS) the TSC increments with the P0 frequency
so the calibration is not needed and booting can be a couple of mcecs
faster on those machines.

Besides, there should be virtually no machines out there which don't
have this bit set, therefore this calibration can be safely removed. It
is a shaky hack anyway since it assumes implicitly that the core is in
P0 when BIOS hands off to the OS, which might not always be the case.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <20100825162823.GE26438@aftab>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index ba5f62f..fc563fa 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -412,6 +412,23 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
 			set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
 	}
 #endif
+
+	/* We need to do the following only once */
+	if (c != &boot_cpu_data)
+		return;
+
+	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
+
+		if (c->x86 > 0x10 ||
+		    (c->x86 == 0x10 && c->x86_model >= 0x2)) {
+			u64 val;
+
+			rdmsrl(MSR_K7_HWCR, val);
+			if (!(val & BIT(24)))
+				printk(KERN_WARNING FW_BUG "TSC doesn't count "
+					"with P0 frequency!\n");
+		}
+	}
 }
 
 static void __cpuinit init_amd(struct cpuinfo_x86 *c)