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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 * Copyright (C) 2008 Kevin D. Kissell, Paralogos sarl
9 */
10#include <linux/clockchips.h>
11#include <linux/interrupt.h>
12#include <linux/percpu.h>
13
14#include <asm/smtc_ipi.h>
15#include <asm/time.h>
16#include <asm/cevt-r4k.h>
17
18/*
19 * Variant clock event timer support for SMTC on MIPS 34K, 1004K
20 * or other MIPS MT cores.
21 *
22 * Notes on SMTC Support:
23 *
24 * SMTC has multiple microthread TCs pretending to be Linux CPUs.
25 * But there's only one Count/Compare pair per VPE, and Compare
26 * interrupts are taken opportunisitically by available TCs
27 * bound to the VPE with the Count register. The new timer
28 * framework provides for global broadcasts, but we really
29 * want VPE-level multicasts for best behavior. So instead
30 * of invoking the high-level clock-event broadcast code,
31 * this version of SMTC support uses the historical SMTC
32 * multicast mechanisms "under the hood", appearing to the
33 * generic clock layer as if the interrupts are per-CPU.
34 *
35 * The approach taken here is to maintain a set of NR_CPUS
36 * virtual timers, and track which "CPU" needs to be alerted
37 * at each event.
38 *
39 * It's unlikely that we'll see a MIPS MT core with more than
40 * 2 VPEs, but we *know* that we won't need to handle more
41 * VPEs than we have "CPUs". So NCPUs arrays of NCPUs elements
42 * is always going to be overkill, but always going to be enough.
43 */
44
45unsigned long smtc_nexttime[NR_CPUS][NR_CPUS];
46static int smtc_nextinvpe[NR_CPUS];
47
48/*
49 * Timestamps stored are absolute values to be programmed
50 * into Count register. Valid timestamps will never be zero.
51 * If a Zero Count value is actually calculated, it is converted
52 * to be a 1, which will introduce 1 or two CPU cycles of error
53 * roughly once every four billion events, which at 1000 HZ means
54 * about once every 50 days. If that's actually a problem, one
55 * could alternate squashing 0 to 1 and to -1.
56 */
57
58#define MAKEVALID(x) (((x) == 0L) ? 1L : (x))
59#define ISVALID(x) ((x) != 0L)
60
61/*
62 * Time comparison is subtle, as it's really truncated
63 * modular arithmetic.
64 */
65
66#define IS_SOONER(a, b, reference) \
67 (((a) - (unsigned long)(reference)) < ((b) - (unsigned long)(reference)))
68
69/*
70 * CATCHUP_INCREMENT, used when the function falls behind the counter.
71 * Could be an increasing function instead of a constant;
72 */
73
74#define CATCHUP_INCREMENT 64
75
76static int mips_next_event(unsigned long delta,
77 struct clock_event_device *evt)
78{
79 unsigned long flags;
80 unsigned int mtflags;
81 unsigned long timestamp, reference, previous;
82 unsigned long nextcomp = 0L;
83 int vpe = current_cpu_data.vpe_id;
84 int cpu = smp_processor_id();
85 local_irq_save(flags);
86 mtflags = dmt();
87
88 /*
89 * Maintain the per-TC virtual timer
90 * and program the per-VPE shared Count register
91 * as appropriate here...
92 */
93 reference = (unsigned long)read_c0_count();
94 timestamp = MAKEVALID(reference + delta);
95 /*
96 * To really model the clock, we have to catch the case
97 * where the current next-in-VPE timestamp is the old
98 * timestamp for the calling CPE, but the new value is
99 * in fact later. In that case, we have to do a full
100 * scan and discover the new next-in-VPE CPU id and
101 * timestamp.
102 */
103 previous = smtc_nexttime[vpe][cpu];
104 if (cpu == smtc_nextinvpe[vpe] && ISVALID(previous)
105 && IS_SOONER(previous, timestamp, reference)) {
106 int i;
107 int soonest = cpu;
108
109 /*
110 * Update timestamp array here, so that new
111 * value gets considered along with those of
112 * other virtual CPUs on the VPE.
113 */
114 smtc_nexttime[vpe][cpu] = timestamp;
115 for_each_online_cpu(i) {
116 if (ISVALID(smtc_nexttime[vpe][i])
117 && IS_SOONER(smtc_nexttime[vpe][i],
118 smtc_nexttime[vpe][soonest], reference)) {
119 soonest = i;
120 }
121 }
122 smtc_nextinvpe[vpe] = soonest;
123 nextcomp = smtc_nexttime[vpe][soonest];
124 /*
125 * Otherwise, we don't have to process the whole array rank,
126 * we just have to see if the event horizon has gotten closer.
127 */
128 } else {
129 if (!ISVALID(smtc_nexttime[vpe][smtc_nextinvpe[vpe]]) ||
130 IS_SOONER(timestamp,
131 smtc_nexttime[vpe][smtc_nextinvpe[vpe]], reference)) {
132 smtc_nextinvpe[vpe] = cpu;
133 nextcomp = timestamp;
134 }
135 /*
136 * Since next-in-VPE may me the same as the executing
137 * virtual CPU, we update the array *after* checking
138 * its value.
139 */
140 smtc_nexttime[vpe][cpu] = timestamp;
141 }
142
143 /*
144 * It may be that, in fact, we don't need to update Compare,
145 * but if we do, we want to make sure we didn't fall into
146 * a crack just behind Count.
147 */
148 if (ISVALID(nextcomp)) {
149 write_c0_compare(nextcomp);
150 ehb();
151 /*
152 * We never return an error, we just make sure
153 * that we trigger the handlers as quickly as
154 * we can if we fell behind.
155 */
156 while ((nextcomp - (unsigned long)read_c0_count())
157 > (unsigned long)LONG_MAX) {
158 nextcomp += CATCHUP_INCREMENT;
159 write_c0_compare(nextcomp);
160 ehb();
161 }
162 }
163 emt(mtflags);
164 local_irq_restore(flags);
165 return 0;
166}
167
168
169void smtc_distribute_timer(int vpe)
170{
171 unsigned long flags;
172 unsigned int mtflags;
173 int cpu;
174 struct clock_event_device *cd;
175 unsigned long nextstamp = 0L;
176 unsigned long reference;
177
178
179repeat:
180 for_each_online_cpu(cpu) {
181 /*
182 * Find virtual CPUs within the current VPE who have
183 * unserviced timer requests whose time is now past.
184 */
185 local_irq_save(flags);
186 mtflags = dmt();
187 if (cpu_data[cpu].vpe_id == vpe &&
188 ISVALID(smtc_nexttime[vpe][cpu])) {
189 reference = (unsigned long)read_c0_count();
190 if ((smtc_nexttime[vpe][cpu] - reference)
191 > (unsigned long)LONG_MAX) {
192 smtc_nexttime[vpe][cpu] = 0L;
193 emt(mtflags);
194 local_irq_restore(flags);
195 /*
196 * We don't send IPIs to ourself.
197 */
198 if (cpu != smp_processor_id()) {
199 smtc_send_ipi(cpu, SMTC_CLOCK_TICK, 0);
200 } else {
201 cd = &per_cpu(mips_clockevent_device, cpu);
202 cd->event_handler(cd);
203 }
204 } else {
205 /* Local to VPE but Valid Time not yet reached. */
206 if (!ISVALID(nextstamp) ||
207 IS_SOONER(smtc_nexttime[vpe][cpu], nextstamp,
208 reference)) {
209 smtc_nextinvpe[vpe] = cpu;
210 nextstamp = smtc_nexttime[vpe][cpu];
211 }
212 emt(mtflags);
213 local_irq_restore(flags);
214 }
215 } else {
216 emt(mtflags);
217 local_irq_restore(flags);
218
219 }
220 }
221 /* Reprogram for interrupt at next soonest timestamp for VPE */
222 if (ISVALID(nextstamp)) {
223 write_c0_compare(nextstamp);
224 ehb();
225 if ((nextstamp - (unsigned long)read_c0_count())
226 > (unsigned long)LONG_MAX)
227 goto repeat;
228 }
229}
230
231
232irqreturn_t c0_compare_interrupt(int irq, void *dev_id)
233{
234 int cpu = smp_processor_id();
235
236 /* If we're running SMTC, we've got MIPS MT and therefore MIPS32R2 */
237 handle_perf_irq(1);
238
239 if (read_c0_cause() & (1 << 30)) {
240 /* Clear Count/Compare Interrupt */
241 write_c0_compare(read_c0_compare());
242 smtc_distribute_timer(cpu_data[cpu].vpe_id);
243 }
244 return IRQ_HANDLED;
245}
246
247
248int __cpuinit mips_clockevent_init(void)
249{
250 uint64_t mips_freq = mips_hpt_frequency;
251 unsigned int cpu = smp_processor_id();
252 struct clock_event_device *cd;
253 unsigned int irq;
254 int i;
255 int j;
256
257 if (!cpu_has_counter || !mips_hpt_frequency)
258 return -ENXIO;
259 if (cpu == 0) {
260 for (i = 0; i < num_possible_cpus(); i++) {
261 smtc_nextinvpe[i] = 0;
262 for (j = 0; j < num_possible_cpus(); j++)
263 smtc_nexttime[i][j] = 0L;
264 }
265 /*
266 * SMTC also can't have the usablility test
267 * run by secondary TCs once Compare is in use.
268 */
269 if (!c0_compare_int_usable())
270 return -ENXIO;
271 }
272
273 /*
274 * With vectored interrupts things are getting platform specific.
275 * get_c0_compare_int is a hook to allow a platform to return the
276 * interrupt number of it's liking.
277 */
278 irq = MIPS_CPU_IRQ_BASE + cp0_compare_irq;
279 if (get_c0_compare_int)
280 irq = get_c0_compare_int();
281
282 cd = &per_cpu(mips_clockevent_device, cpu);
283
284 cd->name = "MIPS";
285 cd->features = CLOCK_EVT_FEAT_ONESHOT;
286
287 /* Calculate the min / max delta */
288 cd->mult = div_sc((unsigned long) mips_freq, NSEC_PER_SEC, 32);
289 cd->shift = 32;
290 cd->max_delta_ns = clockevent_delta2ns(0x7fffffff, cd);
291 cd->min_delta_ns = clockevent_delta2ns(0x300, cd);
292
293 cd->rating = 300;
294 cd->irq = irq;
295 cd->cpumask = cpumask_of_cpu(cpu);
296 cd->set_next_event = mips_next_event;
297 cd->set_mode = mips_set_clock_mode;
298 cd->event_handler = mips_event_handler;
299
300 clockevents_register_device(cd);
301
302 /*
303 * On SMTC we only want to do the data structure
304 * initialization and IRQ setup once.
305 */
306 if (cpu)
307 return 0;
308 /*
309 * And we need the hwmask associated with the c0_compare
310 * vector to be initialized.
311 */
312 irq_hwmask[irq] = (0x100 << cp0_compare_irq);
313 if (cp0_timer_irq_installed)
314 return 0;
315
316 cp0_timer_irq_installed = 1;
317
318 setup_irq(irq, &c0_compare_irqaction);
319
320 return 0;
321}
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