1 /*
2 * This file is subject to the terms and conditions of the GNU General Public
3 * License. See the file "COPYING" in the main directory of this archive
4 * for more details.
5 *
6 * Copyright (C) 2007 MIPS Technologies, Inc.
7 * Copyright (C) 2007 Ralf Baechle <ralf@linux-mips.org>
8 */
9 #include <linux/clockchips.h>
10 #include <linux/interrupt.h>
11 #include <linux/cpufreq.h>
12 #include <linux/percpu.h>
13 #include <linux/smp.h>
14 #include <linux/irq.h>
15
16 #include <asm/time.h>
17 #include <asm/cevt-r4k.h>
18
mips_next_event(unsigned long delta,struct clock_event_device * evt)19 static int mips_next_event(unsigned long delta,
20 struct clock_event_device *evt)
21 {
22 unsigned int cnt;
23 int res;
24
25 cnt = read_c0_count();
26 cnt += delta;
27 write_c0_compare(cnt);
28 res = ((int)(read_c0_count() - cnt) >= 0) ? -ETIME : 0;
29 return res;
30 }
31
32 /**
33 * calculate_min_delta() - Calculate a good minimum delta for mips_next_event().
34 *
35 * Running under virtualisation can introduce overhead into mips_next_event() in
36 * the form of hypervisor emulation of CP0_Count/CP0_Compare registers,
37 * potentially with an unnatural frequency, which makes a fixed min_delta_ns
38 * value inappropriate as it may be too small.
39 *
40 * It can also introduce occasional latency from the guest being descheduled.
41 *
42 * This function calculates a good minimum delta based roughly on the 75th
43 * percentile of the time taken to do the mips_next_event() sequence, in order
44 * to handle potentially higher overhead while also eliminating outliers due to
45 * unpredictable hypervisor latency (which can be handled by retries).
46 *
47 * Return: An appropriate minimum delta for the clock event device.
48 */
calculate_min_delta(void)49 static unsigned int calculate_min_delta(void)
50 {
51 unsigned int cnt, i, j, k, l;
52 unsigned int buf1[4], buf2[3];
53 unsigned int min_delta;
54
55 /*
56 * Calculate the median of 5 75th percentiles of 5 samples of how long
57 * it takes to set CP0_Compare = CP0_Count + delta.
58 */
59 for (i = 0; i < 5; ++i) {
60 for (j = 0; j < 5; ++j) {
61 /*
62 * This is like the code in mips_next_event(), and
63 * directly measures the borderline "safe" delta.
64 */
65 cnt = read_c0_count();
66 write_c0_compare(cnt);
67 cnt = read_c0_count() - cnt;
68
69 /* Sorted insert into buf1 */
70 for (k = 0; k < j; ++k) {
71 if (cnt < buf1[k]) {
72 l = min_t(unsigned int,
73 j, ARRAY_SIZE(buf1) - 1);
74 for (; l > k; --l)
75 buf1[l] = buf1[l - 1];
76 break;
77 }
78 }
79 if (k < ARRAY_SIZE(buf1))
80 buf1[k] = cnt;
81 }
82
83 /* Sorted insert of 75th percentile into buf2 */
84 for (k = 0; k < i && k < ARRAY_SIZE(buf2); ++k) {
85 if (buf1[ARRAY_SIZE(buf1) - 1] < buf2[k]) {
86 l = min_t(unsigned int,
87 i, ARRAY_SIZE(buf2) - 1);
88 for (; l > k; --l)
89 buf2[l] = buf2[l - 1];
90 break;
91 }
92 }
93 if (k < ARRAY_SIZE(buf2))
94 buf2[k] = buf1[ARRAY_SIZE(buf1) - 1];
95 }
96
97 /* Use 2 * median of 75th percentiles */
98 min_delta = buf2[ARRAY_SIZE(buf2) - 1] * 2;
99
100 /* Don't go too low */
101 if (min_delta < 0x300)
102 min_delta = 0x300;
103
104 pr_debug("%s: median 75th percentile=%#x, min_delta=%#x\n",
105 __func__, buf2[ARRAY_SIZE(buf2) - 1], min_delta);
106 return min_delta;
107 }
108
109 DEFINE_PER_CPU(struct clock_event_device, mips_clockevent_device);
110 int cp0_timer_irq_installed;
111
112 /*
113 * Possibly handle a performance counter interrupt.
114 * Return true if the timer interrupt should not be checked
115 */
handle_perf_irq(int r2)116 static inline int handle_perf_irq(int r2)
117 {
118 /*
119 * The performance counter overflow interrupt may be shared with the
120 * timer interrupt (cp0_perfcount_irq < 0). If it is and a
121 * performance counter has overflowed (perf_irq() == IRQ_HANDLED)
122 * and we can't reliably determine if a counter interrupt has also
123 * happened (!r2) then don't check for a timer interrupt.
124 */
125 return (cp0_perfcount_irq < 0) &&
126 perf_irq() == IRQ_HANDLED &&
127 !r2;
128 }
129
c0_compare_interrupt(int irq,void * dev_id)130 irqreturn_t c0_compare_interrupt(int irq, void *dev_id)
131 {
132 const int r2 = cpu_has_mips_r2_r6;
133 struct clock_event_device *cd;
134 int cpu = smp_processor_id();
135
136 /*
137 * Suckage alert:
138 * Before R2 of the architecture there was no way to see if a
139 * performance counter interrupt was pending, so we have to run
140 * the performance counter interrupt handler anyway.
141 */
142 if (handle_perf_irq(r2))
143 return IRQ_HANDLED;
144
145 /*
146 * The same applies to performance counter interrupts. But with the
147 * above we now know that the reason we got here must be a timer
148 * interrupt. Being the paranoiacs we are we check anyway.
149 */
150 if (!r2 || (read_c0_cause() & CAUSEF_TI)) {
151 /* Clear Count/Compare Interrupt */
152 write_c0_compare(read_c0_compare());
153 cd = &per_cpu(mips_clockevent_device, cpu);
154 cd->event_handler(cd);
155
156 return IRQ_HANDLED;
157 }
158
159 return IRQ_NONE;
160 }
161
162 struct irqaction c0_compare_irqaction = {
163 .handler = c0_compare_interrupt,
164 /*
165 * IRQF_SHARED: The timer interrupt may be shared with other interrupts
166 * such as perf counter and FDC interrupts.
167 */
168 .flags = IRQF_PERCPU | IRQF_TIMER | IRQF_SHARED,
169 .name = "timer",
170 };
171
172
mips_event_handler(struct clock_event_device * dev)173 void mips_event_handler(struct clock_event_device *dev)
174 {
175 }
176
177 /*
178 * FIXME: This doesn't hold for the relocated E9000 compare interrupt.
179 */
c0_compare_int_pending(void)180 static int c0_compare_int_pending(void)
181 {
182 /* When cpu_has_mips_r2, this checks Cause.TI instead of Cause.IP7 */
183 return (read_c0_cause() >> cp0_compare_irq_shift) & (1ul << CAUSEB_IP);
184 }
185
186 /*
187 * Compare interrupt can be routed and latched outside the core,
188 * so wait up to worst case number of cycle counter ticks for timer interrupt
189 * changes to propagate to the cause register.
190 */
191 #define COMPARE_INT_SEEN_TICKS 50
192
c0_compare_int_usable(void)193 int c0_compare_int_usable(void)
194 {
195 unsigned int delta;
196 unsigned int cnt;
197
198 /*
199 * IP7 already pending? Try to clear it by acking the timer.
200 */
201 if (c0_compare_int_pending()) {
202 cnt = read_c0_count();
203 write_c0_compare(cnt - 1);
204 back_to_back_c0_hazard();
205 while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
206 if (!c0_compare_int_pending())
207 break;
208 if (c0_compare_int_pending())
209 return 0;
210 }
211
212 for (delta = 0x10; delta <= 0x400000; delta <<= 1) {
213 cnt = read_c0_count();
214 cnt += delta;
215 write_c0_compare(cnt);
216 back_to_back_c0_hazard();
217 if ((int)(read_c0_count() - cnt) < 0)
218 break;
219 /* increase delta if the timer was already expired */
220 }
221
222 while ((int)(read_c0_count() - cnt) <= 0)
223 ; /* Wait for expiry */
224
225 while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
226 if (c0_compare_int_pending())
227 break;
228 if (!c0_compare_int_pending())
229 return 0;
230 cnt = read_c0_count();
231 write_c0_compare(cnt - 1);
232 back_to_back_c0_hazard();
233 while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
234 if (!c0_compare_int_pending())
235 break;
236 if (c0_compare_int_pending())
237 return 0;
238
239 /*
240 * Feels like a real count / compare timer.
241 */
242 return 1;
243 }
244
get_c0_compare_int(void)245 unsigned int __weak get_c0_compare_int(void)
246 {
247 return MIPS_CPU_IRQ_BASE + cp0_compare_irq;
248 }
249
250 #ifdef CONFIG_CPU_FREQ
251
252 static unsigned long mips_ref_freq;
253
r4k_cpufreq_callback(struct notifier_block * nb,unsigned long val,void * data)254 static int r4k_cpufreq_callback(struct notifier_block *nb,
255 unsigned long val, void *data)
256 {
257 struct cpufreq_freqs *freq = data;
258 struct clock_event_device *cd;
259 unsigned long rate;
260 int cpu;
261
262 if (!mips_ref_freq)
263 mips_ref_freq = freq->old;
264
265 if (val == CPUFREQ_POSTCHANGE) {
266 rate = cpufreq_scale(mips_hpt_frequency, mips_ref_freq,
267 freq->new);
268
269 for_each_cpu(cpu, freq->policy->cpus) {
270 cd = &per_cpu(mips_clockevent_device, cpu);
271
272 clockevents_update_freq(cd, rate);
273 }
274 }
275
276 return 0;
277 }
278
279 static struct notifier_block r4k_cpufreq_notifier = {
280 .notifier_call = r4k_cpufreq_callback,
281 };
282
r4k_register_cpufreq_notifier(void)283 static int __init r4k_register_cpufreq_notifier(void)
284 {
285 return cpufreq_register_notifier(&r4k_cpufreq_notifier,
286 CPUFREQ_TRANSITION_NOTIFIER);
287
288 }
289 core_initcall(r4k_register_cpufreq_notifier);
290
291 #endif /* !CONFIG_CPU_FREQ */
292
r4k_clockevent_init(void)293 int r4k_clockevent_init(void)
294 {
295 unsigned long flags = IRQF_PERCPU | IRQF_TIMER | IRQF_SHARED;
296 unsigned int cpu = smp_processor_id();
297 struct clock_event_device *cd;
298 unsigned int irq, min_delta;
299
300 if (!cpu_has_counter || !mips_hpt_frequency)
301 return -ENXIO;
302
303 if (!c0_compare_int_usable())
304 return -ENXIO;
305
306 /*
307 * With vectored interrupts things are getting platform specific.
308 * get_c0_compare_int is a hook to allow a platform to return the
309 * interrupt number of its liking.
310 */
311 irq = get_c0_compare_int();
312
313 cd = &per_cpu(mips_clockevent_device, cpu);
314
315 cd->name = "MIPS";
316 cd->features = CLOCK_EVT_FEAT_ONESHOT |
317 CLOCK_EVT_FEAT_C3STOP |
318 CLOCK_EVT_FEAT_PERCPU;
319
320 min_delta = calculate_min_delta();
321
322 cd->rating = 300;
323 cd->irq = irq;
324 cd->cpumask = cpumask_of(cpu);
325 cd->set_next_event = mips_next_event;
326 cd->event_handler = mips_event_handler;
327
328 clockevents_config_and_register(cd, mips_hpt_frequency, min_delta, 0x7fffffff);
329
330 if (cp0_timer_irq_installed)
331 return 0;
332
333 cp0_timer_irq_installed = 1;
334
335 if (request_irq(irq, c0_compare_interrupt, flags, "timer",
336 c0_compare_interrupt))
337 pr_err("Failed to request irq %d (timer)\n", irq);
338
339 return 0;
340 }
341
342