1 #include <linux/types.h>
2 #include <linux/i8253.h>
3 #include <linux/interrupt.h>
6 #include <linux/time.h>
7 #include <linux/clockchips.h>
12 #define SNI_CLOCK_TICK_RATE 3686400
13 #define SNI_COUNTER2_DIV 64
14 #define SNI_COUNTER0_DIV ((SNI_CLOCK_TICK_RATE / SNI_COUNTER2_DIV) / HZ)
16 static int a20r_set_periodic(struct clock_event_device
*evt
)
18 *(volatile u8
*)(A20R_PT_CLOCK_BASE
+ 12) = 0x34;
20 *(volatile u8
*)(A20R_PT_CLOCK_BASE
+ 0) = SNI_COUNTER0_DIV
;
22 *(volatile u8
*)(A20R_PT_CLOCK_BASE
+ 0) = SNI_COUNTER0_DIV
>> 8;
25 *(volatile u8
*)(A20R_PT_CLOCK_BASE
+ 12) = 0xb4;
27 *(volatile u8
*)(A20R_PT_CLOCK_BASE
+ 8) = SNI_COUNTER2_DIV
;
29 *(volatile u8
*)(A20R_PT_CLOCK_BASE
+ 8) = SNI_COUNTER2_DIV
>> 8;
34 static struct clock_event_device a20r_clockevent_device
= {
36 .features
= CLOCK_EVT_FEAT_PERIODIC
,
38 /* .mult, .shift, .max_delta_ns and .min_delta_ns left uninitialized */
41 .irq
= SNI_A20R_IRQ_TIMER
,
42 .set_state_periodic
= a20r_set_periodic
,
45 static irqreturn_t
a20r_interrupt(int irq
, void *dev_id
)
47 struct clock_event_device
*cd
= dev_id
;
49 *(volatile u8
*)A20R_PT_TIM0_ACK
= 0;
52 cd
->event_handler(cd
);
57 static struct irqaction a20r_irqaction
= {
58 .handler
= a20r_interrupt
,
59 .flags
= IRQF_PERCPU
| IRQF_TIMER
,
64 * a20r platform uses 2 counters to divide the input frequency.
65 * Counter 2 output is connected to Counter 0 & 1 input.
67 static void __init
sni_a20r_timer_setup(void)
69 struct clock_event_device
*cd
= &a20r_clockevent_device
;
70 struct irqaction
*action
= &a20r_irqaction
;
71 unsigned int cpu
= smp_processor_id();
73 cd
->cpumask
= cpumask_of(cpu
);
74 clockevents_register_device(cd
);
76 setup_irq(SNI_A20R_IRQ_TIMER
, &a20r_irqaction
);
79 #define SNI_8254_TICK_RATE 1193182UL
81 #define SNI_8254_TCSAMP_COUNTER ((SNI_8254_TICK_RATE / HZ) + 255)
83 static __init
unsigned long dosample(void)
88 /* Start the counter. */
90 outb_p(SNI_8254_TCSAMP_COUNTER
& 0xff, 0x40);
91 outb(SNI_8254_TCSAMP_COUNTER
>> 8, 0x40);
93 /* Get initial counter invariant */
94 ct0
= read_c0_count();
96 /* Latch and spin until top byte of counter0 is zero */
101 ct1
= read_c0_count();
104 /* Stop the counter. */
107 * Return the difference, this is how far the r4k counter increments
108 * for every 1/HZ seconds. We round off the nearest 1 MHz of master
109 * clock (= 1000000 / HZ / 2).
111 /*return (ct1 - ct0 + (500000/HZ/2)) / (500000/HZ) * (500000/HZ);*/
112 return (ct1
- ct0
) / (500000/HZ
) * (500000/HZ
);
116 * Here we need to calibrate the cycle counter to at least be close.
118 void __init
plat_time_init(void)
120 unsigned long r4k_ticks
[3];
121 unsigned long r4k_tick
;
124 * Figure out the r4k offset, the algorithm is very simple and works in
125 * _all_ cases as long as the 8254 counter register itself works ok (as
126 * an interrupt driving timer it does not because of bug, this is why
127 * we are using the onchip r4k counter/compare register to serve this
128 * purpose, but for r4k_offset calculation it will work ok for us).
129 * There are other very complicated ways of performing this calculation
130 * but this one works just fine so I am not going to futz around. ;-)
132 printk(KERN_INFO
"Calibrating system timer... ");
133 dosample(); /* Prime cache. */
134 dosample(); /* Prime cache. */
135 /* Zero is NOT an option. */
137 r4k_ticks
[0] = dosample();
138 } while (!r4k_ticks
[0]);
140 r4k_ticks
[1] = dosample();
141 } while (!r4k_ticks
[1]);
143 if (r4k_ticks
[0] != r4k_ticks
[1]) {
144 printk("warning: timer counts differ, retrying... ");
145 r4k_ticks
[2] = dosample();
146 if (r4k_ticks
[2] == r4k_ticks
[0]
147 || r4k_ticks
[2] == r4k_ticks
[1])
148 r4k_tick
= r4k_ticks
[2];
150 printk("disagreement, using average... ");
151 r4k_tick
= (r4k_ticks
[0] + r4k_ticks
[1]
155 r4k_tick
= r4k_ticks
[0];
157 printk("%d [%d.%04d MHz CPU]\n", (int) r4k_tick
,
158 (int) (r4k_tick
/ (500000 / HZ
)),
159 (int) (r4k_tick
% (500000 / HZ
)));
161 mips_hpt_frequency
= r4k_tick
* HZ
;
163 switch (sni_brd_type
) {
166 case SNI_BRD_TOWER_OASIC
:
167 case SNI_BRD_MINITOWER
:
168 sni_a20r_timer_setup();
174 void read_persistent_clock(struct timespec
*ts
)