xref: /openbmc/linux/arch/x86/include/asm/mach_timer.h (revision b2441318)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  *  Machine specific calibrate_tsc() for generic.
4  *  Split out from timer_tsc.c by Osamu Tomita <tomita@cinet.co.jp>
5  */
6 /* ------ Calibrate the TSC -------
7  * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
8  * Too much 64-bit arithmetic here to do this cleanly in C, and for
9  * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
10  * output busy loop as low as possible. We avoid reading the CTC registers
11  * directly because of the awkward 8-bit access mechanism of the 82C54
12  * device.
13  */
14 #ifndef _ASM_X86_MACH_DEFAULT_MACH_TIMER_H
15 #define _ASM_X86_MACH_DEFAULT_MACH_TIMER_H
16 
17 #define CALIBRATE_TIME_MSEC 30 /* 30 msecs */
18 #define CALIBRATE_LATCH	\
19 	((PIT_TICK_RATE * CALIBRATE_TIME_MSEC + 1000/2)/1000)
20 
mach_prepare_counter(void)21 static inline void mach_prepare_counter(void)
22 {
23        /* Set the Gate high, disable speaker */
24 	outb((inb(0x61) & ~0x02) | 0x01, 0x61);
25 
26 	/*
27 	 * Now let's take care of CTC channel 2
28 	 *
29 	 * Set the Gate high, program CTC channel 2 for mode 0,
30 	 * (interrupt on terminal count mode), binary count,
31 	 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
32 	 *
33 	 * Some devices need a delay here.
34 	 */
35 	outb(0xb0, 0x43);			/* binary, mode 0, LSB/MSB, Ch 2 */
36 	outb_p(CALIBRATE_LATCH & 0xff, 0x42);	/* LSB of count */
37 	outb_p(CALIBRATE_LATCH >> 8, 0x42);       /* MSB of count */
38 }
39 
mach_countup(unsigned long * count_p)40 static inline void mach_countup(unsigned long *count_p)
41 {
42 	unsigned long count = 0;
43 	do {
44 		count++;
45 	} while ((inb_p(0x61) & 0x20) == 0);
46 	*count_p = count;
47 }
48 
49 #endif /* _ASM_X86_MACH_DEFAULT_MACH_TIMER_H */
50