x86: tsc: Read all ratio bits from MSR_PLATFORM_INFO

Currently we read the tsc radio like this:

	ratio = (MSR_PLATFORM_INFO >> 8) & 0x1f;

Thus we get bit 8-12 of MSR_PLATFORM_INFO, however according to the
Intel manual, the ratio bits are bit 8-15.

Fix this problem by masking 0xff instead.

This keeps in sync with Linux kernel commit:
  886123f: x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

diff --git a/drivers/timer/tsc_timer.c b/drivers/timer/tsc_timer.c
index 5c4ec0018f6860a622d409a6aefd559e2a9496c2..ffbc7091fa24007173b16d9a82cc0cb510af0a0c 100644 (file)
--- a/drivers/timer/tsc_timer.c
+++ b/drivers/timer/tsc_timer.c
@@ -92,7 +92,7 @@ static unsigned long __maybe_unused try_msr_calibrate_tsc(void)
 
        if (freq_desc_tables[cpu_index].msr_plat) {
                rdmsr(MSR_PLATFORM_INFO, lo, hi);
-               ratio = (lo >> 8) & 0x1f;
+               ratio = (lo >> 8) & 0xff;
        } else {
                rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
                ratio = (hi >> 8) & 0x1f;