xref: /netbsd-src/sys/arch/arc/isa/isabus.c (revision 82d56013d7b633d116a93943de88e08335357a7c)
1 /*	$NetBSD: isabus.c,v 1.52 2021/04/24 23:36:25 thorpej Exp $	*/
2 /*	$OpenBSD: isabus.c,v 1.15 1998/03/16 09:38:46 pefo Exp $	*/
3 /*	NetBSD: isa.c,v 1.33 1995/06/28 04:30:51 cgd Exp 	*/
4 
5 /*-
6  * Copyright (c) 1990 The Regents of the University of California.
7  * All rights reserved.
8  *
9  * This code is derived from software contributed to Berkeley by
10  * William Jolitz and Don Ahn.
11  *
12  * Redistribution and use in source and binary forms, with or without
13  * modification, are permitted provided that the following conditions
14  * are met:
15  * 1. Redistributions of source code must retain the above copyright
16  *    notice, this list of conditions and the following disclaimer.
17  * 2. Redistributions in binary form must reproduce the above copyright
18  *    notice, this list of conditions and the following disclaimer in the
19  *    documentation and/or other materials provided with the distribution.
20  * 3. Neither the name of the University nor the names of its contributors
21  *    may be used to endorse or promote products derived from this software
22  *    without specific prior written permission.
23  *
24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34  * SUCH DAMAGE.
35  *
36  *	@(#)isa.c	7.2 (Berkeley) 5/12/91
37  */
38 /*-
39  * Copyright (c) 1995 Per Fogelstrom
40  * Copyright (c) 1993, 1994 Charles M. Hannum.
41  *
42  * This code is derived from software contributed to Berkeley by
43  * William Jolitz and Don Ahn.
44  *
45  * Redistribution and use in source and binary forms, with or without
46  * modification, are permitted provided that the following conditions
47  * are met:
48  * 1. Redistributions of source code must retain the above copyright
49  *    notice, this list of conditions and the following disclaimer.
50  * 2. Redistributions in binary form must reproduce the above copyright
51  *    notice, this list of conditions and the following disclaimer in the
52  *    documentation and/or other materials provided with the distribution.
53  * 3. All advertising materials mentioning features or use of this software
54  *    must display the following acknowledgement:
55  *	This product includes software developed by the University of
56  *	California, Berkeley and its contributors.
57  * 4. Neither the name of the University nor the names of its contributors
58  *    may be used to endorse or promote products derived from this software
59  *    without specific prior written permission.
60  *
61  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
62  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
63  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
64  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
65  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
66  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
67  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
68  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
69  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
70  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
71  * SUCH DAMAGE.
72  *
73  *	@(#)isa.c	7.2 (Berkeley) 5/12/91
74  */
75 /*
76  * Mach Operating System
77  * Copyright (c) 1991,1990,1989 Carnegie Mellon University
78  * All Rights Reserved.
79  *
80  * Permission to use, copy, modify and distribute this software and its
81  * documentation is hereby granted, provided that both the copyright
82  * notice and this permission notice appear in all copies of the
83  * software, derivative works or modified versions, and any portions
84  * thereof, and that both notices appear in supporting documentation.
85  *
86  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
87  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
88  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
89  *
90  * Carnegie Mellon requests users of this software to return to
91  *
92  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
93  *  School of Computer Science
94  *  Carnegie Mellon University
95  *  Pittsburgh PA 15213-3890
96  *
97  * any improvements or extensions that they make and grant Carnegie Mellon
98  * the rights to redistribute these changes.
99  */
100 /*
101   Copyright 1988, 1989 by Intel Corporation, Santa Clara, California.
102 
103 		All Rights Reserved
104 
105 Permission to use, copy, modify, and distribute this software and
106 its documentation for any purpose and without fee is hereby
107 granted, provided that the above copyright notice appears in all
108 copies and that both the copyright notice and this permission notice
109 appear in supporting documentation, and that the name of Intel
110 not be used in advertising or publicity pertaining to distribution
111 of the software without specific, written prior permission.
112 
113 INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
114 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
115 IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
116 CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
117 LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
118 NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
119 WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
120 */
121 
122 #include <sys/cdefs.h>
123 __KERNEL_RCSID(0, "$NetBSD: isabus.c,v 1.52 2021/04/24 23:36:25 thorpej Exp $");
124 
125 #include <sys/param.h>
126 #include <sys/proc.h>
127 #include <sys/systm.h>
128 #include <sys/callout.h>
129 #include <sys/time.h>
130 #include <sys/kernel.h>
131 #include <sys/device.h>
132 #include <sys/kmem.h>
133 #include <sys/extent.h>
134 
135 #include <uvm/uvm_extern.h>
136 
137 #include <machine/cpu.h>
138 #include <machine/pio.h>
139 #include <machine/autoconf.h>
140 #include <machine/intr.h>
141 
142 #include <mips/locore.h>
143 
144 #include <dev/ic/i8253reg.h>
145 #include <dev/ic/i8259reg.h>
146 #include <dev/isa/isareg.h>
147 #include <dev/isa/isavar.h>
148 #include <arc/isa/isabrvar.h>
149 #include <arc/isa/spkrreg.h>
150 
151 #include <arc/arc/timervar.h>
152 
153 static int beeping;
154 static callout_t sysbeep_ch;
155 
156 static long isa_mem_ex_storage[EXTENT_FIXED_STORAGE_SIZE(16) / sizeof(long)];
157 static long isa_io_ex_storage[EXTENT_FIXED_STORAGE_SIZE(16) / sizeof(long)];
158 
159 #define	IRQ_SLAVE	2
160 
161 /* Definition of the driver for autoconfig. */
162 static int isabrprint(void *, const char *);
163 
164 extern struct arc_bus_space arc_bus_io, arc_bus_mem;
165 
166 static void isabr_attach_hook(device_t , device_t,
167     struct isabus_attach_args *);
168 static void isabr_detach_hook(isa_chipset_tag_t, device_t);
169 static const struct evcnt *isabr_intr_evcnt(isa_chipset_tag_t, int);
170 static void *isabr_intr_establish(isa_chipset_tag_t, int, int, int,
171     int (*)(void *), void *);
172 static void isabr_intr_disestablish(isa_chipset_tag_t, void*);
173 static void isabr_initicu(void);
174 static void intr_calculatemasks(void);
175 static int fakeintr(void *a);
176 
177 struct isabr_config *isabr_conf = NULL;
178 uint32_t imask[_IPL_N];	/* XXX */
179 
180 void
181 isabrattach(struct isabr_softc *sc)
182 {
183 	struct isabus_attach_args iba;
184 
185 	callout_init(&sysbeep_ch, 0);
186 
187 	if (isabr_conf == NULL)
188 		panic("isabr_conf isn't initialized");
189 
190 	aprint_normal("\n");
191 
192 	/* Initialize interrupt controller */
193 	isabr_initicu();
194 
195 	sc->arc_isa_cs.ic_attach_hook = isabr_attach_hook;
196 	sc->arc_isa_cs.ic_detach_hook = isabr_detach_hook;
197 	sc->arc_isa_cs.ic_intr_evcnt = isabr_intr_evcnt;
198 	sc->arc_isa_cs.ic_intr_establish = isabr_intr_establish;
199 	sc->arc_isa_cs.ic_intr_disestablish = isabr_intr_disestablish;
200 
201 	arc_bus_space_init_extent(&arc_bus_mem, (void *)isa_mem_ex_storage,
202 	    sizeof(isa_mem_ex_storage));
203 	arc_bus_space_init_extent(&arc_bus_io, (void *)isa_io_ex_storage,
204 	    sizeof(isa_io_ex_storage));
205 
206 	iba.iba_iot = &arc_bus_io;
207 	iba.iba_memt = &arc_bus_mem;
208 	iba.iba_dmat = &sc->sc_dmat;
209 	iba.iba_ic = &sc->arc_isa_cs;
210 	config_found(sc->sc_dev, &iba, isabrprint,
211 	    CFARG_IATTR, "isabus",
212 	    CFARG_EOL);
213 }
214 
215 static int
216 isabrprint(void *aux, const char *pnp)
217 {
218 
219         if (pnp)
220                 aprint_normal("isa at %s", pnp);
221         aprint_verbose(" isa_io_base 0x%"PRIxVADDR" isa_mem_base 0x%"PRIxVADDR,
222 	    arc_bus_io.bs_vbase, arc_bus_mem.bs_vbase);
223         return UNCONF;
224 }
225 
226 
227 /*
228  *	Interrupt system driver code
229  *	============================
230  */
231 #define LEGAL_IRQ(x)    ((x) >= 0 && (x) < ICU_LEN && (x) != 2)
232 
233 int	imen;
234 int	intrtype[ICU_LEN], intrmask[ICU_LEN], intrlevel[ICU_LEN];
235 struct isa_intrhand *isa_intrhand[ICU_LEN];
236 
237 static int
238 fakeintr(void *a)
239 {
240 
241 	return 0;
242 }
243 
244 /*
245  * Recalculate the interrupt masks from scratch.
246  * We could code special registry and deregistry versions of this function that
247  * would be faster, but the code would be nastier, and we don't expect this to
248  * happen very much anyway.
249  */
250 static void
251 intr_calculatemasks(void)
252 {
253 	int irq, level;
254 	struct isa_intrhand *q;
255 
256 	/* First, figure out which levels each IRQ uses. */
257 	for (irq = 0; irq < ICU_LEN; irq++) {
258 		int levels = 0;
259 		for (q = isa_intrhand[irq]; q; q = q->ih_next)
260 			levels |= 1 << q->ih_level;
261 		intrlevel[irq] = levels;
262 	}
263 
264 	/* Then figure out which IRQs use each level. */
265 	for (level = 0; level < _IPL_N; level++) {
266 		int irqs = 0;
267 		for (irq = 0; irq < ICU_LEN; irq++)
268 			if (intrlevel[irq] & (1 << level))
269 				irqs |= 1 << irq;
270 		imask[level] = irqs;
271 	}
272 
273 	imask[IPL_NONE] = 0;
274 
275 	imask[IPL_SOFTCLOCK] |= imask[IPL_NONE];
276 	imask[IPL_SOFTNET] |= imask[IPL_SOFTCLOCK];
277 
278 	/*
279 	 * Enforce a hierarchy that gives slow devices a better chance at not
280 	 * dropping data.
281 	 */
282 	imask[IPL_VM] |= imask[IPL_SOFTNET];
283 
284 	/*
285 	 * Since run queues may be manipulated by both the statclock and tty,
286 	 * network, and diskdrivers, clock > tty.
287 	 */
288 	imask[IPL_SCHED] |= imask[IPL_VM];
289 
290 	/* And eventually calculate the complete masks. */
291 	for (irq = 0; irq < ICU_LEN; irq++) {
292 		int irqs = 1 << irq;
293 		for (q = isa_intrhand[irq]; q; q = q->ih_next)
294 			irqs |= imask[q->ih_level];
295 		intrmask[irq] = irqs;
296 	}
297 
298 	/* Lastly, determine which IRQs are actually in use. */
299 	{
300 		int irqs = 0;
301 		for (irq = 0; irq < ICU_LEN; irq++)
302 			if (isa_intrhand[irq])
303 				irqs |= 1 << irq;
304 		if (irqs >= 0x100) /* any IRQs >= 8 in use */
305 			irqs |= 1 << IRQ_SLAVE;
306 		imen = ~irqs;
307 		isa_outb(IO_ICU1 + PIC_OCW1, imen);
308 		isa_outb(IO_ICU2 + PIC_OCW1, imen >> 8);
309 	}
310 }
311 
312 static void
313 isabr_attach_hook(device_t parent, device_t self,
314     struct isabus_attach_args *iba)
315 {
316 
317 	/* Nothing to do. */
318 }
319 
320 static void
321 isabr_detach_hook(isa_chipset_tag_t ic, device_t self)
322 {
323 
324 	/* Nothing to do. */
325 }
326 
327 static const struct evcnt *
328 isabr_intr_evcnt(isa_chipset_tag_t ic, int irq)
329 {
330 
331 	/* XXX for now, no evcnt parent reported */
332 	return NULL;
333 }
334 
335 /*
336  *	Establish a ISA bus interrupt.
337  */
338 static void *
339 isabr_intr_establish(isa_chipset_tag_t ic, int irq, int type, int level,
340     int (*ih_fun)(void *), void *ih_arg)
341 {
342 	struct isa_intrhand **p, *q, *ih;
343 	static struct isa_intrhand fakehand = {NULL, fakeintr};
344 
345 	ih = kmem_alloc(sizeof *ih, KM_SLEEP);
346 
347 	if (!LEGAL_IRQ(irq) || type == IST_NONE)
348 		panic("intr_establish: bogus irq or type");
349 
350 	switch (intrtype[irq]) {
351 	case IST_NONE:
352 		intrtype[irq] = type;
353 		break;
354 	case IST_EDGE:
355 	case IST_LEVEL:
356 		if (type == intrtype[irq])
357 			break;
358 	case IST_PULSE:
359 		if (type != IST_NONE)
360 			panic("intr_establish: can't share %s with %s",
361 			    isa_intr_typename(intrtype[irq]),
362 			    isa_intr_typename(type));
363 		break;
364 	}
365 
366 	/*
367 	 * Figure out where to put the handler.
368 	 * This is O(N^2), but we want to preserve the order, and N is
369 	 * generally small.
370 	 */
371 	for (p = &isa_intrhand[irq]; (q = *p) != NULL; p = &q->ih_next)
372 		;
373 
374 	/*
375 	 * Actually install a fake handler momentarily, since we might be doing
376 	 * this with interrupts enabled and don't want the real routine called
377 	 * until masking is set up.
378 	 */
379 	fakehand.ih_level = level;
380 	*p = &fakehand;
381 
382 	intr_calculatemasks();
383 
384 	/*
385 	 * Poke the real handler in now.
386 	 */
387 	ih->ih_fun = ih_fun;
388 	ih->ih_arg = ih_arg;
389 	ih->ih_count = 0;
390 	ih->ih_next = NULL;
391 	ih->ih_level = level;
392 	ih->ih_irq = irq;
393 	snprintf(ih->ih_evname, sizeof(ih->ih_evname), "irq %d", irq);
394 	evcnt_attach_dynamic(&ih->ih_evcnt, EVCNT_TYPE_INTR, NULL, "isa",
395 	    ih->ih_evname);
396 	*p = ih;
397 
398 	return ih;
399 }
400 
401 static void
402 isabr_intr_disestablish(isa_chipset_tag_t ic, void *arg)
403 {
404 
405 }
406 
407 /*
408  *	Process an interrupt from the ISA bus.
409  */
410 uint32_t
411 isabr_iointr(uint32_t mask, struct clockframe *cf)
412 {
413 	struct isa_intrhand *ih;
414 	int isa_vector;
415 	int o_imen;
416 
417 	isa_vector = (*isabr_conf->ic_intr_status)();
418 	if (isa_vector < 0)
419 		return 0;
420 
421 	o_imen = imen;
422 	imen |= 1 << (isa_vector & (ICU_LEN - 1));
423 	if (isa_vector & 0x08) {
424 		isa_inb(IO_ICU2 + PIC_OCW1);
425 		isa_outb(IO_ICU2 + PIC_OCW1, imen >> 8);
426 		isa_outb(IO_ICU2 + PIC_OCW2,
427 		    OCW2_SELECT | OCW2_EOI | OCW2_SL |
428 		    OCW2_ILS((isa_vector & 7)));
429 		isa_outb(IO_ICU1,
430 		    OCW2_SELECT | OCW2_EOI | OCW2_SL | IRQ_SLAVE);
431 	} else {
432 		isa_inb(IO_ICU1 + PIC_OCW1);
433 		isa_outb(IO_ICU1 + PIC_OCW1, imen);
434 		isa_outb(IO_ICU1 + PIC_OCW2,
435 		    OCW2_SELECT | OCW2_EOI | OCW2_SL | OCW2_ILS(isa_vector));
436 	}
437 	ih = isa_intrhand[isa_vector];
438 	if (isa_vector == 0 && ih) {	/* Clock */	/*XXX*/
439 		last_cp0_count = mips3_cp0_count_read();
440 		/* XXX: spllowerclock() not allowed */
441 		cf->sr &= ~MIPS_SR_INT_IE;
442 		if ((*ih->ih_fun)(cf))
443 			ih->ih_evcnt.ev_count++;
444 		ih = ih->ih_next;
445 	}
446 	while (ih) {
447 		if ((*ih->ih_fun)(ih->ih_arg))
448 			ih->ih_evcnt.ev_count++;
449 		ih = ih->ih_next;
450 	}
451 	imen = o_imen;
452 	isa_inb(IO_ICU1 + PIC_OCW1);
453 	isa_inb(IO_ICU2 + PIC_OCW1);
454 	isa_outb(IO_ICU1 + PIC_OCW1, imen);
455 	isa_outb(IO_ICU2 + PIC_OCW1, imen >> 8);
456 
457 	return MIPS_INT_MASK_2;
458 }
459 
460 
461 /*
462  * Initialize the Interrupt controller logic.
463  */
464 static void
465 isabr_initicu(void)
466 {
467 
468 	int i;
469 
470 	for (i = 0; i < ICU_LEN; i++) {
471 		switch (i) {
472 		case 2:
473 		case 8:
474 			intrtype[i] = IST_EDGE;
475 			break;
476 		default:
477 			intrtype[i] = IST_NONE;
478 			break;
479 		}
480 	}
481 
482 	/* reset; program device, four bytes */
483 	isa_outb(IO_ICU1 + PIC_ICW1, ICW1_SELECT | ICW1_IC4);
484 	/* starting at this vector index */
485 	isa_outb(IO_ICU1 + PIC_ICW2, 0);
486 	/* slave on line 2 */
487 	isa_outb(IO_ICU1 + PIC_ICW3, ICW3_CASCADE(IRQ_SLAVE));
488 	/* 8086 mode */
489 	isa_outb(IO_ICU1 + PIC_ICW4, ICW4_8086);
490 
491 	/* leave interrupts masked */
492 	isa_outb(IO_ICU1 + PIC_OCW1, 0xff);
493 
494 	/* special mask mode (if available) */
495 	isa_outb(IO_ICU1 + PIC_OCW3, OCW3_SELECT | OCW3_SSMM | OCW3_SMM);
496 	/* Read IRR by default. */
497 	isa_outb(IO_ICU1 + PIC_OCW3, OCW3_SELECT | OCW3_RR);
498 #ifdef REORDER_IRQ
499 	/* pri order 3-7, 0-2 (com2 first) */
500 	isa_outb(IO_ICU1 + PIC_OCW2,
501 	    OCW2_SELECT | OCW2_R | OCW2_SL OCW2_ILS(3 - 1));
502 #endif
503 
504 	/* reset; program device, four bytes */
505 	isa_outb(IO_ICU2 + PIC_ICW1, ICW1_SELECT | ICW1_IC4);
506 	/* staring at this vector index */
507 	isa_outb(IO_ICU2 + PIC_ICW2, 8);
508 	/* slave connected to line 2 of master */
509 	isa_outb(IO_ICU2 + PIC_ICW3, ICW3_SIC(IRQ_SLAVE));
510 	/* 8086 mode */
511 	isa_outb(IO_ICU2 + PIC_ICW4, ICW4_8086);
512 
513 	/* leave interrupts masked */
514 	isa_outb(IO_ICU2 + PIC_OCW1, 0xff);
515 
516 	/* special mask mode (if available) */
517 	isa_outb(IO_ICU2 + PIC_OCW3, OCW3_SELECT | OCW3_SSMM | OCW3_SMM);
518 	/* Read IRR by default. */
519 	isa_outb(IO_ICU2 + PIC_OCW3, OCW3_SELECT | OCW3_RR);
520 }
521 
522 
523 /*
524  *	SPEAKER BEEPER...
525  */
526 void
527 sysbeepstop(void *arg)
528 {
529 	int s;
530 
531 	/* disable counter 2 */
532 	s = splhigh();
533 	isa_outb(PITAUX_PORT, isa_inb(PITAUX_PORT) & ~PIT_SPKR);
534 	splx(s);
535 	beeping = 0;
536 }
537 
538 void
539 sysbeep(int pitch, int period)
540 {
541 	static int last_pitch, last_period;
542 	int s;
543 
544 	if (cold)
545 		return;		/* Can't beep yet. */
546 
547 	if (beeping)
548 		callout_stop(&sysbeep_ch);
549 	if (!beeping || last_pitch != pitch) {
550 		s = splhigh();
551 		isa_outb(IO_TIMER1 + TIMER_MODE,
552 		    TIMER_SEL2 | TIMER_16BIT | TIMER_SQWAVE);
553 		isa_outb(IO_TIMER1 + TIMER_CNTR2, TIMER_DIV(pitch) % 256);
554 		isa_outb(IO_TIMER1 + TIMER_CNTR2, TIMER_DIV(pitch) / 256);
555 		isa_outb(PITAUX_PORT, isa_inb(PITAUX_PORT) | PIT_SPKR);
556 		splx(s);
557 	}
558 	last_pitch = pitch;
559 	beeping = last_period = period;
560 	callout_reset(&sysbeep_ch, period, sysbeepstop, NULL);
561 }
562 
563 int
564 isa_intr_alloc(isa_chipset_tag_t c, int mask, int type, int *irq_p)
565 {
566 	int irq;
567 	int maybe_irq = -1;
568 	int shared_depth = 0;
569 	mask &= 0x8b28; /* choose from 3, 5, 8, 9, 11, 15 XXX */
570 	for (irq = 0; mask != 0; mask >>= 1, irq++) {
571 		if ((mask & 1) == 0)
572 			continue;
573 		if (intrtype[irq] == IST_NONE) {
574 			*irq_p = irq;
575 			return 0;
576 		}
577 		/* Level interrupts can be shared */
578 		if (type == IST_LEVEL && intrtype[irq] == IST_LEVEL) {
579 			struct isa_intrhand *ih = isa_intrhand[irq];
580 			int depth;
581 			if (maybe_irq == -1) {
582  				maybe_irq = irq;
583 				continue;
584 			}
585 			for (depth = 0; ih != NULL; ih = ih->ih_next)
586 				depth++;
587 			if (depth < shared_depth) {
588 				maybe_irq = irq;
589 				shared_depth = depth;
590 			}
591 		}
592 	}
593 	if (maybe_irq != -1) {
594 		*irq_p = maybe_irq;
595 		return 0;
596 	}
597 	return 1;
598 }
599