1/*
2 * linux/arch/arm/mach-at91/at91rm9200_time.c
3 *
4 *  Copyright (C) 2003 SAN People
5 *  Copyright (C) 2003 ATMEL
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
20 */
21
22#include <linux/init.h>
23#include <linux/interrupt.h>
24#include <linux/irq.h>
25#include <linux/kernel.h>
26#include <linux/sched.h>
27#include <linux/time.h>
28
29#include <asm/hardware.h>
30#include <asm/io.h>
31#include <asm/mach/time.h>
32
33#include <asm/arch/at91_st.h>
34
35static unsigned long last_crtr;
36
37/*
38 * The ST_CRTR is updated asynchronously to the master clock.  It is therefore
39 *  necessary to read it twice (with the same value) to ensure accuracy.
40 */
41static inline unsigned long read_CRTR(void) {
42	unsigned long x1, x2;
43
44	do {
45		x1 = at91_sys_read(AT91_ST_CRTR);
46		x2 = at91_sys_read(AT91_ST_CRTR);
47	} while (x1 != x2);
48
49	return x1;
50}
51
52/*
53 * Returns number of microseconds since last timer interrupt.  Note that interrupts
54 * will have been disabled by do_gettimeofday()
55 *  'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy.
56 *  'tick' is usecs per jiffy (linux/timex.h).
57 */
58static unsigned long at91rm9200_gettimeoffset(void)
59{
60	unsigned long elapsed;
61
62	elapsed = (read_CRTR() - last_crtr) & AT91_ST_ALMV;
63
64	return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH;
65}
66
67/*
68 * IRQ handler for the timer.
69 */
70static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
71{
72	if (at91_sys_read(AT91_ST_SR) & AT91_ST_PITS) {	/* This is a shared interrupt */
73		write_seqlock(&xtime_lock);
74
75		while (((read_CRTR() - last_crtr) & AT91_ST_ALMV) >= LATCH) {
76			timer_tick();
77			last_crtr = (last_crtr + LATCH) & AT91_ST_ALMV;
78		}
79
80		write_sequnlock(&xtime_lock);
81
82		return IRQ_HANDLED;
83	}
84	else
85		return IRQ_NONE;		/* not handled */
86}
87
88static struct irqaction at91rm9200_timer_irq = {
89	.name		= "at91_tick",
90	.flags		= IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
91	.handler	= at91rm9200_timer_interrupt
92};
93
94void at91rm9200_timer_reset(void)
95{
96	last_crtr = 0;
97
98	/* Real time counter incremented every 30.51758 microseconds */
99	at91_sys_write(AT91_ST_RTMR, 1);
100
101	/* Set Period Interval timer */
102	at91_sys_write(AT91_ST_PIMR, LATCH);
103
104	/* Clear any pending interrupts */
105	(void) at91_sys_read(AT91_ST_SR);
106
107	/* Enable Period Interval Timer interrupt */
108	at91_sys_write(AT91_ST_IER, AT91_ST_PITS);
109}
110
111/*
112 * Set up timer interrupt.
113 */
114void __init at91rm9200_timer_init(void)
115{
116	/* Disable all timer interrupts */
117	at91_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
118	(void) at91_sys_read(AT91_ST_SR);	/* Clear any pending interrupts */
119
120	/* Make IRQs happen for the system timer */
121	setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq);
122
123	/* Change the kernel's 'tick' value to 10009 usec. (the default is 10000) */
124	tick_usec = (LATCH * 1000000) / CLOCK_TICK_RATE;
125
126	/* Initialize and enable the timer interrupt */
127	at91rm9200_timer_reset();
128}
129
130#ifdef CONFIG_PM
131static void at91rm9200_timer_suspend(void)
132{
133	/* disable Period Interval Timer interrupt */
134	at91_sys_write(AT91_ST_IDR, AT91_ST_PITS);
135}
136#else
137#define at91rm9200_timer_suspend	NULL
138#endif
139
140struct sys_timer at91rm9200_timer = {
141	.init		= at91rm9200_timer_init,
142	.offset		= at91rm9200_gettimeoffset,
143	.suspend	= at91rm9200_timer_suspend,
144	.resume		= at91rm9200_timer_reset,
145};
146