linux-kernel - [PATCH 1/2] x86/apb_timer: drop unused TSC calibration

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Date:   Wed, 13 May 2020 12:09:43 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>
Subject: [PATCH 1/2] x86/apb_timer: drop unused TSC calibration

Drop the APB-timer TSC calibration, which hasn't been used since the
removal of Moorestown support by commit 1a8359e411eb ("x86/mid: Remove
Intel Moorestown").

Signed-off-by: Johan Hovold <johan@...nel.org>
---
 arch/x86/include/asm/apb_timer.h |  2 --
 arch/x86/kernel/apb_timer.c      | 53 --------------------------------
 2 files changed, 55 deletions(-)

diff --git a/arch/x86/include/asm/apb_timer.h b/arch/x86/include/asm/apb_timer.h
index 99bb207fc04c..0a9bf8b77a28 100644
--- a/arch/x86/include/asm/apb_timer.h
+++ b/arch/x86/include/asm/apb_timer.h
@@ -28,7 +28,6 @@
 #define APBT_DEV_USED  1
 
 extern void apbt_time_init(void);
-extern unsigned long apbt_quick_calibrate(void);
 extern int arch_setup_apbt_irqs(int irq, int trigger, int mask, int cpu);
 extern void apbt_setup_secondary_clock(void);
 
@@ -38,7 +37,6 @@ extern int sfi_mtimer_num;
 
 #else /* CONFIG_APB_TIMER */
 
-static inline unsigned long apbt_quick_calibrate(void) {return 0; }
 static inline void apbt_time_init(void) { }
 
 #endif
diff --git a/arch/x86/kernel/apb_timer.c b/arch/x86/kernel/apb_timer.c
index fe698f96617c..263eeaddb0aa 100644
--- a/arch/x86/kernel/apb_timer.c
+++ b/arch/x86/kernel/apb_timer.c
@@ -345,56 +345,3 @@ void __init apbt_time_init(void)
 	apb_timer_block_enabled = 0;
 	panic("failed to enable APB timer\n");
 }
-
-/* called before apb_timer_enable, use early map */
-unsigned long apbt_quick_calibrate(void)
-{
-	int i, scale;
-	u64 old, new;
-	u64 t1, t2;
-	unsigned long khz = 0;
-	u32 loop, shift;
-
-	apbt_set_mapping();
-	dw_apb_clocksource_start(clocksource_apbt);
-
-	/* check if the timer can count down, otherwise return */
-	old = dw_apb_clocksource_read(clocksource_apbt);
-	i = 10000;
-	while (--i) {
-		if (old != dw_apb_clocksource_read(clocksource_apbt))
-			break;
-	}
-	if (!i)
-		goto failed;
-
-	/* count 16 ms */
-	loop = (apbt_freq / 1000) << 4;
-
-	/* restart the timer to ensure it won't get to 0 in the calibration */
-	dw_apb_clocksource_start(clocksource_apbt);
-
-	old = dw_apb_clocksource_read(clocksource_apbt);
-	old += loop;
-
-	t1 = rdtsc();
-
-	do {
-		new = dw_apb_clocksource_read(clocksource_apbt);
-	} while (new < old);
-
-	t2 = rdtsc();
-
-	shift = 5;
-	if (unlikely(loop >> shift == 0)) {
-		printk(KERN_INFO
-		       "APBT TSC calibration failed, not enough resolution\n");
-		return 0;
-	}
-	scale = (int)div_u64((t2 - t1), loop >> shift);
-	khz = (scale * (apbt_freq / 1000)) >> shift;
-	printk(KERN_INFO "TSC freq calculated by APB timer is %lu khz\n", khz);
-	return khz;
-failed:
-	return 0;
-}
-- 
2.26.2