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isabus.c revision 1.29
      1 /*	$NetBSD: isabus.c,v 1.29 2005/10/30 05:27:14 tsutsui 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 (at) 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 1.29 2005/10/30 05:27:14 tsutsui Exp $");
    124 
    125 #include <sys/param.h>
    126 #include <sys/proc.h>
    127 #include <sys/user.h>
    128 #include <sys/systm.h>
    129 #include <sys/callout.h>
    130 #include <sys/time.h>
    131 #include <sys/kernel.h>
    132 #include <sys/device.h>
    133 #include <sys/malloc.h>
    134 #include <sys/extent.h>
    135 
    136 #include <uvm/uvm_extern.h>
    137 
    138 #include <machine/cpu.h>
    139 #include <machine/pio.h>
    140 #include <machine/autoconf.h>
    141 #include <machine/intr.h>
    142 
    143 #include <mips/locore.h>
    144 
    145 #include <dev/ic/i8253reg.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 struct callout sysbeep_ch = CALLOUT_INITIALIZER;
    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 int	isabrprint(void *, const char *);
    163 
    164 extern struct arc_bus_space arc_bus_io, arc_bus_mem;
    165 
    166 void	isabr_attach_hook(struct device *, struct device *,
    167 			struct isabus_attach_args *);
    168 const struct evcnt *isabr_intr_evcnt(isa_chipset_tag_t, int);
    169 void	*isabr_intr_establish(isa_chipset_tag_t, int, int, int,
    170 			int (*)(void *), void *);
    171 void	isabr_intr_disestablish(isa_chipset_tag_t, void*);
    172 uint32_t isabr_iointr(uint32_t, struct clockframe *);
    173 void	isabr_initicu(void);
    174 void	intr_calculatemasks(void);
    175 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 	if (isabr_conf == NULL)
    186 		panic("isabr_conf isn't initialized");
    187 
    188 	printf("\n");
    189 
    190 	/* Initialize interrupt controller */
    191 	isabr_initicu();
    192 
    193 /*XXX we may remove the abus part of the softc struct... */
    194 	sc->sc_bus.ab_dv = (struct device *)sc;
    195 	sc->sc_bus.ab_type = BUS_ISABR;
    196 
    197 	sc->arc_isa_cs.ic_attach_hook = isabr_attach_hook;
    198 	sc->arc_isa_cs.ic_intr_evcnt = isabr_intr_evcnt;
    199 	sc->arc_isa_cs.ic_intr_establish = isabr_intr_establish;
    200 	sc->arc_isa_cs.ic_intr_disestablish = isabr_intr_disestablish;
    201 
    202 	arc_bus_space_init_extent(&arc_bus_mem, (caddr_t)isa_mem_ex_storage,
    203 	    sizeof(isa_mem_ex_storage));
    204 	arc_bus_space_init_extent(&arc_bus_io, (caddr_t)isa_io_ex_storage,
    205 	    sizeof(isa_io_ex_storage));
    206 
    207 	iba.iba_iot = &arc_bus_io;
    208 	iba.iba_memt = &arc_bus_mem;
    209 	iba.iba_dmat = &sc->sc_dmat;
    210 	iba.iba_ic = &sc->arc_isa_cs;
    211 	config_found_ia(&sc->sc_dev, "isabus", &iba, isabrprint);
    212 }
    213 
    214 int
    215 isabrprint(void *aux, const char *pnp)
    216 {
    217 
    218         if (pnp)
    219                 aprint_normal("isa at %s", pnp);
    220         aprint_verbose(" isa_io_base 0x%lx isa_mem_base 0x%lx",
    221 		arc_bus_io.bs_vbase, arc_bus_mem.bs_vbase);
    222         return (UNCONF);
    223 }
    224 
    225 
    226 /*
    227  *	Interrupt system driver code
    228  *	============================
    229  */
    230 #define LEGAL_IRQ(x)    ((x) >= 0 && (x) < ICU_LEN && (x) != 2)
    231 
    232 int	imen;
    233 int	intrtype[ICU_LEN], intrmask[ICU_LEN], intrlevel[ICU_LEN];
    234 struct intrhand *intrhand[ICU_LEN];
    235 
    236 int fakeintr(void *a)
    237 {
    238 
    239 	return 0;
    240 }
    241 
    242 /*
    243  * Recalculate the interrupt masks from scratch.
    244  * We could code special registry and deregistry versions of this function that
    245  * would be faster, but the code would be nastier, and we don't expect this to
    246  * happen very much anyway.
    247  */
    248 void
    249 intr_calculatemasks(void)
    250 {
    251 	int irq, level;
    252 	struct intrhand *q;
    253 
    254 	/* First, figure out which levels each IRQ uses. */
    255 	for (irq = 0; irq < ICU_LEN; irq++) {
    256 		int levels = 0;
    257 		for (q = intrhand[irq]; q; q = q->ih_next)
    258 			levels |= 1 << q->ih_level;
    259 		intrlevel[irq] = levels;
    260 	}
    261 
    262 	/* Then figure out which IRQs use each level. */
    263 	for (level = 0; level < _IPL_N; level++) {
    264 		int irqs = 0;
    265 		for (irq = 0; irq < ICU_LEN; irq++)
    266 			if (intrlevel[irq] & (1 << level))
    267 				irqs |= 1 << irq;
    268 		imask[level] = irqs;
    269 	}
    270 
    271 	imask[IPL_NONE] = 0;
    272 
    273 	imask[IPL_SOFT] |= imask[IPL_NONE];
    274 	imask[IPL_SOFTCLOCK] |= imask[IPL_SOFT];
    275 	imask[IPL_SOFTNET] |= imask[IPL_SOFTCLOCK];
    276 	imask[IPL_SOFTSERIAL] |= imask[IPL_SOFTNET];
    277 
    278 	/*
    279 	 * Enforce a hierarchy that gives slow devices a better chance at not
    280 	 * dropping data.
    281 	 */
    282 	imask[IPL_BIO] |= imask[IPL_SOFTSERIAL];
    283 	imask[IPL_NET] |= imask[IPL_BIO];
    284 	imask[IPL_TTY] |= imask[IPL_NET];
    285 
    286 	/*
    287 	 * Since run queues may be manipulated by both the statclock and tty,
    288 	 * network, and diskdrivers, clock > tty.
    289 	 */
    290 	imask[IPL_CLOCK] |= imask[IPL_TTY];
    291 	imask[IPL_STATCLOCK] |= imask[IPL_CLOCK];
    292 
    293 	/*
    294 	 * IPL_HIGH must block everything that can manipulate a run queue.
    295 	 */
    296 	imask[IPL_HIGH] |= imask[IPL_STATCLOCK];
    297 
    298 	/* And eventually calculate the complete masks. */
    299 	for (irq = 0; irq < ICU_LEN; irq++) {
    300 		int irqs = 1 << irq;
    301 		for (q = intrhand[irq]; q; q = q->ih_next)
    302 			irqs |= imask[q->ih_level];
    303 		intrmask[irq] = irqs;
    304 	}
    305 
    306 	/* Lastly, determine which IRQs are actually in use. */
    307 	{
    308 		int irqs = 0;
    309 		for (irq = 0; irq < ICU_LEN; irq++)
    310 			if (intrhand[irq])
    311 				irqs |= 1 << irq;
    312 		if (irqs >= 0x100) /* any IRQs >= 8 in use */
    313 			irqs |= 1 << IRQ_SLAVE;
    314 		imen = ~irqs;
    315 		isa_outb(IO_ICU1 + 1, imen);
    316 		isa_outb(IO_ICU2 + 1, imen >> 8);
    317 	}
    318 }
    319 
    320 void
    321 isabr_attach_hook(struct device *parent, struct device *self,
    322     struct isabus_attach_args *iba)
    323 {
    324 
    325 	/* Nothing to do. */
    326 }
    327 
    328 const struct evcnt *
    329 isabr_intr_evcnt(isa_chipset_tag_t ic, int irq)
    330 {
    331 
    332 	/* XXX for now, no evcnt parent reported */
    333 	return NULL;
    334 }
    335 
    336 /*
    337  *	Establish a ISA bus interrupt.
    338  */
    339 void *
    340 isabr_intr_establish(isa_chipset_tag_t ic, int irq, int type, int level,
    341     int (*ih_fun)(void *), void *ih_arg)
    342 {
    343 	struct intrhand **p, *q, *ih;
    344 	static struct intrhand fakehand = {NULL, fakeintr};
    345 
    346 	/* no point in sleeping unless someone can free memory. */
    347 	ih = malloc(sizeof *ih, M_DEVBUF, cold ? M_NOWAIT : M_WAITOK);
    348 	if (ih == NULL)
    349 		panic("isa_intr_establish: can't malloc handler info");
    350 
    351 	if (!LEGAL_IRQ(irq) || type == IST_NONE)
    352 		panic("intr_establish: bogus irq or type");
    353 
    354 	switch (intrtype[irq]) {
    355 	case IST_NONE:
    356 		intrtype[irq] = type;
    357 		break;
    358 	case IST_EDGE:
    359 	case IST_LEVEL:
    360 		if (type == intrtype[irq])
    361 			break;
    362 	case IST_PULSE:
    363 		if (type != IST_NONE)
    364 			panic("intr_establish: can't share %s with %s",
    365 			    isa_intr_typename(intrtype[irq]),
    366 			    isa_intr_typename(type));
    367 		break;
    368 	}
    369 
    370 	/*
    371 	 * Figure out where to put the handler.
    372 	 * This is O(N^2), but we want to preserve the order, and N is
    373 	 * generally small.
    374 	 */
    375 	for (p = &intrhand[irq]; (q = *p) != NULL; p = &q->ih_next)
    376 		;
    377 
    378 	/*
    379 	 * Actually install a fake handler momentarily, since we might be doing
    380 	 * this with interrupts enabled and don't want the real routine called
    381 	 * until masking is set up.
    382 	 */
    383 	fakehand.ih_level = level;
    384 	*p = &fakehand;
    385 
    386 	intr_calculatemasks();
    387 
    388 	/*
    389 	 * Poke the real handler in now.
    390 	 */
    391 	ih->ih_fun = ih_fun;
    392 	ih->ih_arg = ih_arg;
    393 	ih->ih_count = 0;
    394 	ih->ih_next = NULL;
    395 	ih->ih_level = level;
    396 	ih->ih_irq = irq;
    397 	ih->ih_what = ""; /* XXX - should be eliminated */
    398 	*p = ih;
    399 
    400 	return ih;
    401 }
    402 
    403 void
    404 isabr_intr_disestablish(isa_chipset_tag_t ic, void *arg)
    405 {
    406 
    407 }
    408 
    409 /*
    410  *	Process an interrupt from the ISA bus.
    411  */
    412 uint32_t
    413 isabr_iointr(uint32_t mask, struct clockframe *cf)
    414 {
    415 	struct intrhand *ih;
    416 	int isa_vector;
    417 	int o_imen;
    418 
    419 	isa_vector = (*isabr_conf->ic_intr_status)();
    420 	if (isa_vector < 0)
    421 		return (~0);
    422 
    423 	o_imen = imen;
    424 	imen |= 1 << (isa_vector & (ICU_LEN - 1));
    425 	if (isa_vector & 0x08) {
    426 		isa_inb(IO_ICU2 + 1);
    427 		isa_outb(IO_ICU2 + 1, imen >> 8);
    428 		isa_outb(IO_ICU2, 0x60 + (isa_vector & 7));
    429 		isa_outb(IO_ICU1, 0x60 + IRQ_SLAVE);
    430 	} else {
    431 		isa_inb(IO_ICU1 + 1);
    432 		isa_outb(IO_ICU1 + 1, imen);
    433 		isa_outb(IO_ICU1, 0x60 + isa_vector);
    434 	}
    435 	ih = intrhand[isa_vector];
    436 	if (isa_vector == 0) {	/* Clock */	/*XXX*/
    437 		last_cp0_count = mips3_cp0_count_read();
    438 		(*ih->ih_fun)(cf);
    439 		ih = ih->ih_next;
    440 	}
    441 	while (ih) {
    442 		(*ih->ih_fun)(ih->ih_arg);
    443 		ih = ih->ih_next;
    444 	}
    445 	imen = o_imen;
    446 	isa_inb(IO_ICU1 + 1);
    447 	isa_inb(IO_ICU2 + 1);
    448 	isa_outb(IO_ICU1 + 1, imen);
    449 	isa_outb(IO_ICU2 + 1, imen >> 8);
    450 
    451 	return ~0;  /* Dont reenable */
    452 }
    453 
    454 
    455 /*
    456  * Initialize the Interrupt controller logic.
    457  */
    458 void
    459 isabr_initicu(void)
    460 {
    461 
    462 	int i;
    463 
    464 	for (i = 0; i < ICU_LEN; i++) {
    465 		switch (i) {
    466 		case 2:
    467 		case 8:
    468 			intrtype[i] = IST_EDGE;
    469 			break;
    470 		default:
    471 			intrtype[i] = IST_NONE;
    472 			break;
    473 		}
    474 	}
    475 
    476 	isa_outb(IO_ICU1, 0x11);		/* reset; program device, four bytes */
    477 	isa_outb(IO_ICU1+1, 0);			/* starting at this vector index */
    478 	isa_outb(IO_ICU1+1, 1 << IRQ_SLAVE);	/* slave on line 2 */
    479 	isa_outb(IO_ICU1+1, 1);			/* 8086 mode */
    480 	isa_outb(IO_ICU1+1, 0xff);		/* leave interrupts masked */
    481 	isa_outb(IO_ICU1, 0x68);		/* special mask mode (if available) */
    482 	isa_outb(IO_ICU1, 0x0a);		/* Read IRR by default. */
    483 #ifdef REORDER_IRQ
    484 	isa_outb(IO_ICU1, 0xc0 | (3 - 1));	/* pri order 3-7, 0-2 (com2 first) */
    485 #endif
    486 
    487 	isa_outb(IO_ICU2, 0x11);		/* reset; program device, four bytes */
    488 	isa_outb(IO_ICU2+1, 8);			/* staring at this vector index */
    489 	isa_outb(IO_ICU2+1, IRQ_SLAVE);
    490 	isa_outb(IO_ICU2+1, 1);			/* 8086 mode */
    491 	isa_outb(IO_ICU2+1, 0xff);		/* leave interrupts masked */
    492 	isa_outb(IO_ICU2, 0x68);		/* special mask mode (if available) */
    493 	isa_outb(IO_ICU2, 0x0a);		/* Read IRR by default. */
    494 }
    495 
    496 
    497 /*
    498  *	SPEAKER BEEPER...
    499  */
    500 void
    501 sysbeepstop(void *arg)
    502 {
    503 	int s;
    504 
    505 	/* disable counter 2 */
    506 	s = splhigh();
    507 	isa_outb(PITAUX_PORT, isa_inb(PITAUX_PORT) & ~PIT_SPKR);
    508 	splx(s);
    509 	beeping = 0;
    510 }
    511 
    512 void
    513 sysbeep(int pitch, int period)
    514 {
    515 	static int last_pitch, last_period;
    516 	int s;
    517 
    518 	if (cold)
    519 		return;		/* Can't beep yet. */
    520 
    521 	if (beeping)
    522 		callout_stop(&sysbeep_ch);
    523 	if (!beeping || last_pitch != pitch) {
    524 		s = splhigh();
    525 		isa_outb(IO_TIMER1 + TIMER_MODE,
    526 		    TIMER_SEL2 | TIMER_16BIT | TIMER_SQWAVE);
    527 		isa_outb(IO_TIMER1 + TIMER_CNTR2, TIMER_DIV(pitch) % 256);
    528 		isa_outb(IO_TIMER1 + TIMER_CNTR2, TIMER_DIV(pitch) / 256);
    529 		isa_outb(PITAUX_PORT, isa_inb(PITAUX_PORT) | PIT_SPKR);
    530 		splx(s);
    531 	}
    532 	last_pitch = pitch;
    533 	beeping = last_period = period;
    534 	callout_reset(&sysbeep_ch, period, sysbeepstop, NULL);
    535 }
    536 
    537 int
    538 isa_intr_alloc(isa_chipset_tag_t c, int mask, int type, int *irq_p)
    539 {
    540 	int irq;
    541 	int maybe_irq = -1;
    542 	int shared_depth = 0;
    543 	mask &= 0x8b28; /* choose from 3, 5, 8, 9, 11, 15 XXX */
    544 	for (irq = 0; mask != 0; mask >>= 1, irq++) {
    545 		if ((mask & 1) == 0)
    546 			continue;
    547 		if (intrtype[irq] == IST_NONE) {
    548 			*irq_p = irq;
    549 			return 0;
    550 		}
    551 		/* Level interrupts can be shared */
    552 		if (type == IST_LEVEL && intrtype[irq] == IST_LEVEL) {
    553 			struct intrhand *ih = intrhand[irq];
    554 			int depth;
    555 			if (maybe_irq == -1) {
    556  				maybe_irq = irq;
    557 				continue;
    558 			}
    559 			for (depth = 0; ih != NULL; ih = ih->ih_next)
    560 				depth++;
    561 			if (depth < shared_depth) {
    562 				maybe_irq = irq;
    563 				shared_depth = depth;
    564 			}
    565 		}
    566 	}
    567 	if (maybe_irq != -1) {
    568 		*irq_p = maybe_irq;
    569 		return 0;
    570 	}
    571 	return 1;
    572 }
    573