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pciide.c revision 1.8
      1 /*	$NetBSD: pciide.c,v 1.8 1998/08/14 20:35:40 drochner Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1996, 1998 Christopher G. Demetriou.  All rights reserved.
      5  *
      6  * Redistribution and use in source and binary forms, with or without
      7  * modification, are permitted provided that the following conditions
      8  * are met:
      9  * 1. Redistributions of source code must retain the above copyright
     10  *    notice, this list of conditions and the following disclaimer.
     11  * 2. Redistributions in binary form must reproduce the above copyright
     12  *    notice, this list of conditions and the following disclaimer in the
     13  *    documentation and/or other materials provided with the distribution.
     14  * 3. All advertising materials mentioning features or use of this software
     15  *    must display the following acknowledgement:
     16  *      This product includes software developed by Christopher G. Demetriou
     17  *	for the NetBSD Project.
     18  * 4. The name of the author may not be used to endorse or promote products
     19  *    derived from this software without specific prior written permission
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     22  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     23  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     24  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     25  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     26  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     27  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     28  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     29  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     30  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     31  */
     32 
     33 /*
     34  * PCI IDE controller driver.
     35  *
     36  * Author: Christopher G. Demetriou, March 2, 1998 (derived from NetBSD
     37  * sys/dev/pci/ppb.c, revision 1.16).
     38  *
     39  * See "PCI IDE Controller Specification, Revision 1.0 3/4/94" and
     40  * "Programming Interface for Bus Master IDE Controller, Revision 1.0
     41  * 5/16/94" from the PCI SIG.
     42  *
     43  * XXX Does not yet support DMA (but does map the Bus Master DMA regs).
     44  *
     45  * XXX Does not support serializing the two channels for broken (at least
     46  * XXX according to linux and freebsd) controllers, e.g. CMD PCI0640.
     47  */
     48 
     49 #include <sys/param.h>
     50 #include <sys/systm.h>
     51 #include <sys/device.h>
     52 
     53 #include <dev/pci/pcireg.h>
     54 #include <dev/pci/pcivar.h>
     55 #include <dev/pci/pciidereg.h>
     56 #include <dev/pci/pciidevar.h>
     57 #include <dev/ic/wdcreg.h>
     58 
     59 struct pciide_softc {
     60 	struct device		sc_dev;
     61 
     62 	void			*sc_pci_ih;	/* PCI interrupt handle */
     63 	int			sc_dma_ok;	/* bus-master DMA info */
     64 	bus_space_tag_t		sc_dma_iot;
     65 	bus_space_handle_t	sc_dma_ioh;
     66 
     67 	struct pciide_channel {			/* per-channel data */
     68 		/* internal bookkeeping */
     69 		int		hw_ok;		/* hardware mapped & OK? */
     70 		struct device	*dev;		/* 'wdc' dev attached */
     71 		int		compat;		/* is it compat? */
     72 		void		*ih;		/* compat or pci handle */
     73 
     74 		/* used by wdc attachment (read-only after init) */
     75 		bus_space_tag_t	cmd_iot, ctl_iot;
     76 		bus_space_handle_t cmd_ioh, ctl_ioh;
     77 
     78 		/* filled in by wdc attachment (written by wdc attach) */
     79 		int		(*ihand) __P((void *));
     80 		void		*ihandarg;
     81 	} sc_channels[PCIIDE_NUM_CHANNELS];
     82 };
     83 
     84 #define	PCIIDE_CHANNEL_NAME(chan)	((chan) == 0 ? "primary" : "secondary")
     85 
     86 int	pciide_match __P((struct device *, struct cfdata *, void *));
     87 void	pciide_attach __P((struct device *, struct device *, void *));
     88 
     89 struct cfattach pciide_ca = {
     90 	sizeof(struct pciide_softc), pciide_match, pciide_attach
     91 };
     92 
     93 int	pciide_map_channel_compat __P((struct pciide_softc *,
     94 	    struct pci_attach_args *, int));
     95 const char *pciide_compat_channel_probe __P((struct pciide_softc *,
     96 	    struct pci_attach_args *, int));
     97 static int pciide_wdc_regcheck __P((struct pciide_channel *));
     98 int	pciide_probe_wdc __P((struct pciide_channel *));
     99 int	pciide_map_channel_native __P((struct pciide_softc *,
    100 	    struct pci_attach_args *, int));
    101 int	pciide_print __P((void *, const char *pnp));
    102 int	pciide_compat_intr __P((void *));
    103 int	pciide_pci_intr __P((void *));
    104 
    105 #define	PCIIDE_PROBE_WDC_DELAY	100		/* 100us each */
    106 #define	PCIIDE_PROBE_WDC_NDELAY	10000		/* wait up to 1s */
    107 
    108 int
    109 pciide_match(parent, match, aux)
    110 	struct device *parent;
    111 	struct cfdata *match;
    112 	void *aux;
    113 {
    114 	struct pci_attach_args *pa = aux;
    115 
    116 	/*
    117 	 * Check the ID register to see that it's a PCI IDE controller.
    118 	 * If it is, we assume that we can deal with it; it _should_
    119 	 * work in a standardized way...
    120 	 */
    121 	if (PCI_CLASS(pa->pa_class) == PCI_CLASS_MASS_STORAGE &&
    122 	    PCI_SUBCLASS(pa->pa_class) == PCI_SUBCLASS_MASS_STORAGE_IDE) {
    123 		return (1);
    124 	}
    125 
    126 	return (0);
    127 }
    128 
    129 void
    130 pciide_attach(parent, self, aux)
    131 	struct device *parent, *self;
    132 	void *aux;
    133 {
    134 	struct pci_attach_args *pa = aux;
    135 	pci_chipset_tag_t pc = pa->pa_pc;
    136 	struct pciide_softc *sc = (struct pciide_softc *)self;
    137 	struct pciide_attach_args aa;
    138 	struct pciide_channel *cp;
    139 	pcireg_t class, interface, csr;
    140 	pci_intr_handle_t intrhandle;
    141 	const char *intrstr;
    142 	char devinfo[256];
    143 	int i;
    144 
    145 	pci_devinfo(pa->pa_id, pa->pa_class, 0, devinfo);
    146 	printf(": %s (rev. 0x%02x)\n", devinfo, PCI_REVISION(pa->pa_class));
    147 
    148 	if ((pa->pa_flags & PCI_FLAGS_IO_ENABLED) == 0) {
    149 		csr = pci_conf_read(pc, pa->pa_tag, PCI_COMMAND_STATUS_REG);
    150 		printf("%s: device disabled (at %s)\n", sc->sc_dev.dv_xname,
    151 		    (csr & PCI_COMMAND_IO_ENABLE) == 0 ? "device" : "bridge");
    152 		return;
    153 	}
    154 
    155 	class = pci_conf_read(pc, pa->pa_tag, PCI_CLASS_REG);
    156 	interface = PCI_INTERFACE(class);
    157 
    158 	/*
    159 	 * Set up PCI interrupt.
    160 	 *
    161 	 * If mapping fails, that's (probably) because there's no pin
    162 	 * set to intr, which is (probably) because it's a compat-only
    163 	 * device (or hard-wired in compatibility-only mode).  Native-PCI
    164 	 * channels will complain later if the interrupt was needed.
    165 	 *
    166 	 * If establishment fails, that's (probably) some other problem.
    167 	 */
    168 	if (pci_intr_map(pa->pa_pc, pa->pa_intrtag, pa->pa_intrpin,
    169 	    pa->pa_intrline, &intrhandle) == 0) {
    170 		intrstr = pci_intr_string(pa->pa_pc, intrhandle);
    171 		sc->sc_pci_ih = pci_intr_establish(pa->pa_pc, intrhandle,
    172 		    IPL_BIO, pciide_pci_intr, sc);
    173 
    174 		if (sc->sc_pci_ih != NULL) {
    175 			printf("%s: using %s for native-PCI interrupt\n",
    176 			    sc->sc_dev.dv_xname,
    177 			    intrstr ? intrstr : "unknown interrupt");
    178 		} else {
    179 			printf("%s: couldn't establish native-PCI interrupt",
    180 			    sc->sc_dev.dv_xname);
    181 			if (intrstr != NULL)
    182 				printf(" at %s", intrstr);
    183 			printf("\n");
    184 		}
    185 	}
    186 
    187 	/*
    188 	 * Map DMA registers, if DMA is supported.
    189 	 *
    190 	 * Note that sc_dma_ok is the right variable to test to see if
    191 	 * DMA can * be done.  If the interface doesn't support DMA,
    192 	 * sc_dma_ok * will never be non-zero.  If the DMA regs couldn't
    193 	 * be mapped, it'll be zero.  I.e., sc_dma_ok will only be
    194 	 * non-zero if the interface supports DMA and the registers
    195 	 * could be mapped.
    196 	 *
    197 	 * XXX Note that despite the fact that the Bus Master IDE specs
    198 	 * XXX say that "The bus master IDE functoin uses 16 bytes of IO
    199 	 * XXX space," some controllers (at least the United
    200 	 * XXX Microelectronics UM8886BF) place it in memory space.
    201 	 * XXX eventually, we should probably read the register and check
    202 	 * XXX which type it is.  Either that or 'quirk' certain devices.
    203 	 */
    204 	if (interface & PCIIDE_INTERFACE_BUS_MASTER_DMA) {
    205 		sc->sc_dma_ok = (pci_mapreg_map(pa,
    206 		    PCIIDE_REG_BUS_MASTER_DMA, PCI_MAPREG_TYPE_IO, 0,
    207 		    &sc->sc_dma_iot, &sc->sc_dma_ioh, NULL, NULL) == 0);
    208 		printf("%s: bus-master DMA support present, but unused (%s)\n",
    209 		    sc->sc_dev.dv_xname,
    210 		    sc->sc_dma_ok ? "no driver support" :
    211 		      "couldn't map registers");
    212 	}
    213 
    214 	for (i = 0; i < PCIIDE_NUM_CHANNELS; i++) {
    215 		cp = &sc->sc_channels[i];
    216 
    217 		printf("%s: %s channel %s to %s mode\n",
    218 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(i),
    219 		    (interface & PCIIDE_INTERFACE_SETTABLE(i)) ?
    220 		      "configured" : "wired",
    221 		    (interface & PCIIDE_INTERFACE_PCI(i)) ? "native-PCI" :
    222 		      "compatibility");
    223 
    224 		if (interface & PCIIDE_INTERFACE_PCI(i))
    225 			cp->hw_ok = pciide_map_channel_native(sc, pa, i);
    226 		else
    227 			cp->hw_ok = pciide_map_channel_compat(sc, pa, i);
    228 		if (!cp->hw_ok)
    229 			continue;
    230 
    231 		aa.channel = i;
    232 		aa.cmd_iot = cp->cmd_iot;
    233 		aa.cmd_ioh = cp->cmd_ioh;
    234 		aa.ctl_iot = cp->ctl_iot;
    235 		aa.ctl_ioh = cp->ctl_ioh;
    236 		aa.ihandp = &cp->ihand;
    237 		aa.ihandargp = &cp->ihandarg;
    238 		cp->dev = config_found(self, &aa, pciide_print);
    239 
    240 		/*
    241 		 * Note that if the 'wdc' device isn't configured,
    242 		 * the controller's resources are still marked as
    243 		 * being in use.  This is a feature.
    244 		 */
    245 	}
    246 }
    247 
    248 int
    249 pciide_map_channel_compat(sc, pa, chan)
    250 	struct pciide_softc *sc;
    251 	struct pci_attach_args *pa;
    252 	int chan;
    253 {
    254 	struct pciide_channel *cp = &sc->sc_channels[chan];
    255 	const char *probe_fail_reason;
    256 	int rv = 1;
    257 
    258 	cp->compat = 1;
    259 
    260 	cp->cmd_iot = pa->pa_iot;
    261 	if (bus_space_map(cp->cmd_iot, PCIIDE_COMPAT_CMD_BASE(chan),
    262 	    PCIIDE_COMPAT_CMD_SIZE, 0, &cp->cmd_ioh) != 0) {
    263 		printf("%s: couldn't map %s channel cmd regs\n",
    264 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(chan));
    265 		rv = 0;
    266 	}
    267 
    268 	cp->ctl_iot = pa->pa_iot;
    269 	if (bus_space_map(cp->ctl_iot, PCIIDE_COMPAT_CTL_BASE(chan),
    270 	    PCIIDE_COMPAT_CTL_SIZE, 0, &cp->ctl_ioh) != 0) {
    271 		printf("%s: couldn't map %s channel ctl regs\n",
    272 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(chan));
    273 		rv = 0;
    274 	}
    275 
    276 	/*
    277 	 * If we weren't able to map the device successfully,
    278 	 * we just give up now.  Something else has already
    279 	 * occupied those ports, indicating that the device has
    280 	 * (probably) been completely disabled (by some nonstandard
    281 	 * mechanism).
    282 	 *
    283 	 * XXX If we successfully map some ports, but not others,
    284 	 * XXX it might make sense to unmap the ones that we mapped.
    285 	 */
    286 	if (rv == 0)
    287 		goto out;
    288 
    289 	/*
    290 	 * If we were able to map the device successfully, try to
    291 	 * make sure that there's a wdc there and that it's
    292 	 * attributable to us.
    293 	 *
    294 	 * If there's not, then we assume that there's the device
    295 	 * has been disabled and that other devices are free to use
    296 	 * its ports.
    297 	 */
    298 	probe_fail_reason = pciide_compat_channel_probe(sc, pa, chan);
    299 	if (probe_fail_reason != NULL) {
    300 		printf("%s: %s channel ignored (%s)\n", sc->sc_dev.dv_xname,
    301 		    PCIIDE_CHANNEL_NAME(chan), probe_fail_reason);
    302 		rv = 0;
    303 
    304 		bus_space_unmap(cp->cmd_iot, cp->cmd_ioh,
    305 		    PCIIDE_COMPAT_CMD_SIZE);
    306 		bus_space_unmap(cp->ctl_iot, cp->ctl_ioh,
    307 		    PCIIDE_COMPAT_CTL_SIZE);
    308 
    309 		goto out;
    310 	}
    311 
    312 	/*
    313 	 * If we're here, we were able to map the device successfully
    314 	 * and it really looks like there's a controller there.
    315 	 *
    316 	 * Unless those conditions are true, we don't map the
    317 	 * compatibility interrupt.  The spec indicates that if a
    318 	 * channel is configured for compatibility mode and the PCI
    319 	 * device's I/O space is enabled, the channel will be enabled.
    320 	 * Hoewver, some devices seem to be able to disable invididual
    321 	 * compatibility channels (via non-standard mechanisms).  If
    322 	 * the channel is disabled, the interrupt line can (probably)
    323 	 * be used by other devices (and may be assigned to other
    324 	 * devices by the BIOS).  If we mapped the interrupt we might
    325 	 * conflict with another interrupt assignment.
    326 	 */
    327 	cp->ih = pciide_machdep_compat_intr_establish(&sc->sc_dev, pa,
    328 	    chan, pciide_compat_intr, cp);
    329 	if (cp->ih == NULL) {
    330 		printf("%s: no compatibility interrupt for use by %s channel\n",
    331 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(chan));
    332 		rv = 0;
    333 	}
    334 
    335 out:
    336 	return (rv);
    337 }
    338 
    339 const char *
    340 pciide_compat_channel_probe(sc, pa, chan)
    341 	struct pciide_softc *sc;
    342 	struct pci_attach_args *pa;
    343 {
    344 	pcireg_t csr;
    345 	const char *failreason = NULL;
    346 
    347 	/*
    348 	 * Check to see if something appears to be there.
    349 	 */
    350 	if (!pciide_probe_wdc(&sc->sc_channels[chan])) {
    351 		failreason = "not responding; disabled or no drives?";
    352 		goto out;
    353 	}
    354 
    355 	/*
    356 	 * Now, make sure it's actually attributable to this PCI IDE
    357 	 * channel by trying to access the channel again while the
    358 	 * PCI IDE controller's I/O space is disabled.  (If the
    359 	 * channel no longer appears to be there, it belongs to
    360 	 * this controller.)  YUCK!
    361 	 */
    362 	csr = pci_conf_read(pa->pa_pc, pa->pa_tag, PCI_COMMAND_STATUS_REG);
    363 	pci_conf_write(pa->pa_pc, pa->pa_tag, PCI_COMMAND_STATUS_REG,
    364 	    csr & ~PCI_COMMAND_IO_ENABLE);
    365 	if (pciide_probe_wdc(&sc->sc_channels[chan]))
    366 		failreason = "other hardware responding at addresses";
    367 	pci_conf_write(pa->pa_pc, pa->pa_tag, PCI_COMMAND_STATUS_REG, csr);
    368 
    369 out:
    370 	return (failreason);
    371 }
    372 
    373 /*
    374  * Check writability of wd_cyl_lo and non-writability of wd_error.
    375  * (wd_error in the middle to catch cases where the last written
    376  *  value sticks on the bus)
    377  */
    378 static int
    379 pciide_wdc_regcheck(cp)
    380 	struct pciide_channel *cp;
    381 {
    382 
    383 	bus_space_write_1(cp->cmd_iot, cp->cmd_ioh, wd_cyl_lo, 0xa5);
    384 	bus_space_write_1(cp->cmd_iot, cp->cmd_ioh, wd_error, 0x5a);
    385 	if (bus_space_read_1(cp->cmd_iot, cp->cmd_ioh, wd_error) == 0x5a ||
    386 	    bus_space_read_1(cp->cmd_iot, cp->cmd_ioh, wd_cyl_lo) != 0xa5)
    387 		return (0);
    388 
    389 	return (1);
    390 }
    391 
    392 int
    393 pciide_probe_wdc(cp)
    394 	struct pciide_channel *cp;
    395 {
    396 	int masterprobe, slaveprobe;
    397 	u_int8_t st;
    398 	int timeout;
    399 
    400 	/*
    401 	 * Sanity check to see if the wdc channel responds at all.
    402 	 * (Modeled on wdc_init_controller() and wdc_reset() in wdc.c.)
    403 	 *
    404 	 * Reset the channel, and make sure that it responds sanely
    405 	 * after it's been reset.
    406 	 */
    407 
    408         /* Reset the channel. */
    409         bus_space_write_1(cp->ctl_iot, cp->ctl_ioh, wd_aux_ctlr,
    410             WDCTL_RST | WDCTL_IDS);
    411         delay(1000);
    412         bus_space_write_1(cp->ctl_iot, cp->ctl_ioh, wd_aux_ctlr,
    413             WDCTL_IDS);
    414         delay(1000);
    415         (void)bus_space_read_1(cp->cmd_iot, cp->cmd_ioh, wd_error);
    416 
    417 	masterprobe = slaveprobe = 1;
    418 	timeout = 0;
    419 	while (timeout++ < PCIIDE_PROBE_WDC_NDELAY) {
    420 		if (masterprobe) {
    421 			bus_space_write_1(cp->cmd_iot, cp->cmd_ioh, wd_sdh,
    422 					  WDSD_IBM);
    423 			st = bus_space_read_1(cp->cmd_iot, cp->cmd_ioh,
    424 					      wd_status);
    425 			if ((st & WDCS_BSY) == 0) {
    426 				if (pciide_wdc_regcheck(cp))
    427 					return (1);
    428 				else
    429 					masterprobe = 0;
    430 			}
    431 		}
    432 		if (slaveprobe) {
    433 			bus_space_write_1(cp->cmd_iot, cp->cmd_ioh, wd_sdh,
    434 					  WDSD_IBM | 0x10);
    435 			st = bus_space_read_1(cp->cmd_iot, cp->cmd_ioh,
    436 					      wd_status);
    437 			if ((st & WDCS_BSY) == 0) {
    438 				if (pciide_wdc_regcheck(cp))
    439 					return (1);
    440 				else
    441 					slaveprobe = 0;
    442 			}
    443 		}
    444 
    445 		if (!(masterprobe || slaveprobe))
    446 			break;
    447 
    448 		delay(PCIIDE_PROBE_WDC_DELAY);
    449 	}
    450 
    451 	return (0);
    452 }
    453 
    454 int
    455 pciide_map_channel_native(sc, pa, chan)
    456 	struct pciide_softc *sc;
    457 	struct pci_attach_args *pa;
    458 	int chan;
    459 {
    460 	struct pciide_channel *cp = &sc->sc_channels[chan];
    461 	int rv = 1;
    462 
    463 	cp->compat = 0;
    464 
    465 	if (pci_mapreg_map(pa, PCIIDE_REG_CMD_BASE(chan), PCI_MAPREG_TYPE_IO,
    466 	    0, &cp->cmd_iot, &cp->cmd_ioh, NULL, NULL) != 0) {
    467 		printf("%s: couldn't map %s channel cmd regs\n",
    468 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(chan));
    469 		rv = 0;
    470 	}
    471 
    472 	if (pci_mapreg_map(pa, PCIIDE_REG_CTL_BASE(chan), PCI_MAPREG_TYPE_IO,
    473 	    0, &cp->ctl_iot, &cp->ctl_ioh, NULL, NULL) != 0) {
    474 		printf("%s: couldn't map %s channel ctl regs\n",
    475 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(chan));
    476 		rv = 0;
    477 	}
    478 
    479 	if ((cp->ih = sc->sc_pci_ih) == NULL) {
    480 		printf("%s: no native-PCI interrupt for use by %s channel\n",
    481 		    sc->sc_dev.dv_xname, PCIIDE_CHANNEL_NAME(chan));
    482 		rv = 0;
    483 	}
    484 
    485 	return (rv);
    486 }
    487 
    488 int
    489 pciide_print(aux, pnp)
    490 	void *aux;
    491 	const char *pnp;
    492 {
    493 	struct pciide_attach_args *aa = aux;
    494 
    495 	/* only 'wdc's can attach to 'pciide's; easy. */
    496 	if (pnp)
    497 		printf("wdc at %s", pnp);
    498 	printf(" channel %d", aa->channel);
    499 	return (UNCONF);
    500 }
    501 
    502 int
    503 pciide_compat_intr(arg)
    504 	void *arg;
    505 {
    506 	struct pciide_channel *cp = arg;
    507 
    508 #ifdef DIAGNOSTIC
    509 	/* should only be called for a compat channel */
    510 	if (cp->compat == 0)
    511 		panic("pciide compat intr called for non-compat chan %p\n", cp);
    512 #endif
    513 	/* if there's no handler, that probably means no dev attached */
    514 	if (cp->ihand == NULL)
    515 		return (0);
    516 
    517 	return ((*cp->ihand)(cp->ihandarg));
    518 }
    519 
    520 int
    521 pciide_pci_intr(arg)
    522 	void *arg;
    523 {
    524 	struct pciide_softc *sc = arg;
    525 	struct pciide_channel *cp;
    526 	int i, rv, crv;
    527 
    528 	rv = 0;
    529 	for (i = 0; i < PCIIDE_NUM_CHANNELS; i++) {
    530 		cp = &sc->sc_channels[i];
    531 
    532 		/* If a compat channel or there's no handler, skip. */
    533 		if (cp->compat || cp->ihand == NULL)
    534 			continue;
    535 
    536 		crv = ((*cp->ihand)(cp->ihandarg));
    537 		if (crv == 0)
    538 			;		/* leave rv alone */
    539 		else if (crv == 1)
    540 			rv = 1;		/* claim the intr */
    541 		else if (rv == 0)	/* crv should be -1 in this case */
    542 			rv = crv;	/* if we've done no better, take it */
    543 	}
    544 	return (rv);
    545 }
    546