1 /*
2 * OR1K timer synchronisation
3 *
4 * Based on work from MIPS implementation.
5 *
6 * All CPUs will have their count registers synchronised to the CPU0 next time
7 * value. This can cause a small timewarp for CPU0. All other CPU's should
8 * not have done anything significant (but they may have had interrupts
9 * enabled briefly - prom_smp_finish() should not be responsible for enabling
10 * interrupts...)
11 */
12
13 #include <linux/kernel.h>
14 #include <linux/irqflags.h>
15 #include <linux/cpumask.h>
16
17 #include <asm/time.h>
18 #include <asm/timex.h>
19 #include <linux/atomic.h>
20 #include <asm/barrier.h>
21
22 #include <asm/spr.h>
23
24 static unsigned int initcount;
25 static atomic_t count_count_start = ATOMIC_INIT(0);
26 static atomic_t count_count_stop = ATOMIC_INIT(0);
27
28 #define COUNTON 100
29 #define NR_LOOPS 3
30
31 void synchronise_count_master(int cpu)
32 {
33 int i;
34 unsigned long flags;
35
36 pr_info("Synchronize counters for CPU %u: ", cpu);
37
38 local_irq_save(flags);
39
40 /*
41 * We loop a few times to get a primed instruction cache,
42 * then the last pass is more or less synchronised and
43 * the master and slaves each set their cycle counters to a known
44 * value all at once. This reduces the chance of having random offsets
45 * between the processors, and guarantees that the maximum
46 * delay between the cycle counters is never bigger than
47 * the latency of information-passing (cachelines) between
48 * two CPUs.
49 */
50
51 for (i = 0; i < NR_LOOPS; i++) {
52 /* slaves loop on '!= 2' */
53 while (atomic_read(&count_count_start) != 1)
54 mb();
55 atomic_set(&count_count_stop, 0);
56 smp_wmb();
57
58 /* Let the slave writes its count register */
59 atomic_inc(&count_count_start);
60
61 /* Count will be initialised to current timer */
62 if (i == 1)
63 initcount = get_cycles();
64
65 /*
66 * Everyone initialises count in the last loop:
67 */
68 if (i == NR_LOOPS-1)
69 openrisc_timer_set(initcount);
70
71 /*
72 * Wait for slave to leave the synchronization point:
73 */
74 while (atomic_read(&count_count_stop) != 1)
75 mb();
76 atomic_set(&count_count_start, 0);
77 smp_wmb();
78 atomic_inc(&count_count_stop);
79 }
80 /* Arrange for an interrupt in a short while */
81 openrisc_timer_set_next(COUNTON);
82
83 local_irq_restore(flags);
84
85 /*
86 * i386 code reported the skew here, but the
87 * count registers were almost certainly out of sync
88 * so no point in alarming people
89 */
90 pr_cont("done.\n");
91 }
92
93 void synchronise_count_slave(int cpu)
94 {
95 int i;
96
97 /*
98 * Not every cpu is online at the time this gets called,
99 * so we first wait for the master to say everyone is ready
100 */
101
102 for (i = 0; i < NR_LOOPS; i++) {
103 atomic_inc(&count_count_start);
104 while (atomic_read(&count_count_start) != 2)
105 mb();
106
107 /*
108 * Everyone initialises count in the last loop:
109 */
110 if (i == NR_LOOPS-1)
111 openrisc_timer_set(initcount);
112
113 atomic_inc(&count_count_stop);
114 while (atomic_read(&count_count_stop) != 2)
115 mb();
116 }
117 /* Arrange for an interrupt in a short while */
118 openrisc_timer_set_next(COUNTON);
119 }
120 #undef NR_LOOPS