linux-kernel - [tip:x86/debug] x86/timers: Add simple udelay calibration

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Date:   Tue, 21 Mar 2017 05:19:25 -0700
From:   tip-bot for Lu Baolu <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     bp@...en8.de, dvlasenk@...hat.com, tglx@...utronix.de,
        peterz@...radead.org, brgerst@...il.com,
        mathias.nyman@...ux.intel.com, mingo@...nel.org, hpa@...or.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        jpoimboe@...hat.com, luto@...nel.org,
        torvalds@...ux-foundation.org, baolu.lu@...ux.intel.com
Subject: [tip:x86/debug] x86/timers: Add simple udelay calibration

Commit-ID:  dd759d93f4dd4fd2f345a78ad1223bb3edf3ee7b
Gitweb:     http://git.kernel.org/tip/dd759d93f4dd4fd2f345a78ad1223bb3edf3ee7b
Author:     Lu Baolu <baolu.lu@...ux.intel.com>
AuthorDate: Tue, 21 Mar 2017 16:01:29 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 21 Mar 2017 12:28:45 +0100

x86/timers: Add simple udelay calibration

Add a simple udelay calibration in x86 architecture-specific
boot-time initializations. This will get a workable estimate
for loops_per_jiffy. Hence, udelay() could be used after this
initialization.

Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: linux-usb@...r.kernel.org
Link: http://lkml.kernel.org/r/1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/setup.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 4bf0c89..e70204e 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -837,6 +837,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
 	return 0;
 }
 
+static void __init simple_udelay_calibration(void)
+{
+	unsigned int tsc_khz, cpu_khz;
+	unsigned long lpj;
+
+	if (!boot_cpu_has(X86_FEATURE_TSC))
+		return;
+
+	cpu_khz = x86_platform.calibrate_cpu();
+	tsc_khz = x86_platform.calibrate_tsc();
+
+	tsc_khz = tsc_khz ? : cpu_khz;
+	if (!tsc_khz)
+		return;
+
+	lpj = tsc_khz * 1000;
+	do_div(lpj, HZ);
+	loops_per_jiffy = lpj;
+}
+
 /*
  * Determine if we were loaded by an EFI loader.  If so, then we have also been
  * passed the efi memmap, systab, etc., so we should use these data structures
@@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	x86_configure_nx();
 
+	simple_udelay_calibration();
+
 	parse_early_param();
 
 #ifdef CONFIG_MEMORY_HOTPLUG