From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755079AbcFQFXj (ORCPT ); Fri, 17 Jun 2016 01:23:39 -0400 Received: from mail-qk0-f194.google.com ([209.85.220.194]:33901 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754958AbcFQFXh (ORCPT ); Fri, 17 Jun 2016 01:23:37 -0400 From: Len Brown To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, Len Brown , Bin Gao Subject: [PATCH 10/10] x86 tsc: enumerate BXT tsc_khz via CPUID Date: Fri, 17 Jun 2016 01:22:52 -0400 Message-Id: X-Mailer: git-send-email 2.9.0 In-Reply-To: <20160617052252.25991-1-lenb@kernel.org> References: <20160617052252.25991-1-lenb@kernel.org> In-Reply-To: <2199d0e959f7f71a18827268b5d060f8d3831639.1466138954.git.len.brown@intel.com> References: <2199d0e959f7f71a18827268b5d060f8d3831639.1466138954.git.len.brown@intel.com> Reply-To: Len Brown Organization: Intel Open Source Technology Center Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Len Brown Hard code the BXT crystal clock (aka ART - Always Running Timer) to 19.200 MHz, and use CPUID leaf 0x15 to determine the BXT TSC frequency. Use tsc_khz to sanity check BXT cpu_khz, which can be erroneous in some configurations. Signed-off-by: Bin Gao [lenb: simplified] Signed-off-by: Len Brown --- arch/x86/kernel/tsc.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index e1496b7..2a952fc 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -693,7 +693,11 @@ unsigned long native_calibrate_tsc(void) switch (boot_cpu_data.x86_model) { case 0x4E: /* SKL */ case 0x5E: /* SKL */ - crystal_khz = 24000; /* 24 MHz */ + crystal_khz = 24000; /* 24.0 MHz */ + break; + case 0x5C: /* BXT */ + crystal_khz = 19200; /* 19.2 MHz */ + break; } } @@ -895,6 +899,8 @@ int recalibrate_cpu_khz(void) tsc_khz = x86_platform.calibrate_tsc(); if (tsc_khz == 0) tsc_khz = cpu_khz; + else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz) + cpu_khz = tsc_khz; cpu_data(0).loops_per_jiffy = cpufreq_scale(cpu_data(0).loops_per_jiffy, cpu_khz_old, cpu_khz); @@ -1302,8 +1308,16 @@ void __init tsc_init(void) cpu_khz = x86_platform.calibrate_cpu(); tsc_khz = x86_platform.calibrate_tsc(); + + /* + * Trust non-zero tsc_khz as authorative, + * and use it to sanity check cpu_khz, + * which will be off if system timer is off. + */ if (tsc_khz == 0) tsc_khz = cpu_khz; + else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz) + cpu_khz = tsc_khz; if (!tsc_khz) { mark_tsc_unstable("could not calculate TSC khz"); -- 2.9.0