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

  1a8359e ("x86/mid: Remove Intel Moorestown").

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200513100944.9171-1-johan@kernel.org

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

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;
-}