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 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 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