xref: /freebsd/sys/dev/sound/pcm/dsp.c (revision 4d25c041fe3a08f457824a787c3db7b2ffe394e0)
1 /*
2  * Copyright (c) 1999 Cameron Grant <gandalf@vilnya.demon.co.uk>
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  *
26  * $FreeBSD$
27  */
28 
29 #include <sys/param.h>
30 #include <sys/queue.h>
31 #include <sys/kernel.h>
32 
33 #include <dev/sound/pcm/sound.h>
34 
35 static int getchns(snddev_info *d, int chan, pcm_channel **rdch, pcm_channel **wrch);
36 
37 static pcm_channel *
38 allocchn(snddev_info *d, int direction)
39 {
40 	pcm_channel *chns = (direction == PCMDIR_PLAY)? d->play : d->rec;
41 	int i, cnt = (direction == PCMDIR_PLAY)? d->playcount : d->reccount;
42 	for (i = 0; i < cnt; i++) {
43 		if (!(chns[i].flags & CHN_F_BUSY)) {
44 			chns[i].flags |= CHN_F_BUSY;
45 			return &chns[i];
46 		}
47 	}
48 	return NULL;
49 }
50 
51 static int
52 getchns(snddev_info *d, int chan, pcm_channel **rdch, pcm_channel **wrch)
53 {
54 	if ((d->flags & SD_F_PRIO_SET) == SD_F_PRIO_SET)
55 		panic("read and write both prioritised");
56 	if (d->flags & SD_F_SIMPLEX) {
57 		*rdch = (d->flags & SD_F_PRIO_RD)? d->arec[chan] : &d->fakechan;
58 		*wrch = (d->flags & SD_F_PRIO_WR)? d->aplay[chan] : &d->fakechan;
59 	} else {
60 		*rdch = d->arec[chan];
61 		*wrch = d->aplay[chan];
62 	}
63 	return 0;
64 }
65 
66 static void
67 setchns(snddev_info *d, int chan)
68 {
69 	if ((d->flags & SD_F_PRIO_SET) == SD_F_PRIO_SET)
70 		panic("read and write both prioritised");
71 	d->flags |= SD_F_DIR_SET;
72 	if (d->flags & SD_F_EVILSB16) {
73 		if ((d->flags & SD_F_PRIO_RD) && (d->aplay[chan])) {
74 			pcm_channel *tmp;
75 			tmp = d->arec[chan];
76 			d->arec[chan] = d->aplay[chan];
77 			d->aplay[chan] = tmp;
78 		}
79 		if (d->aplay[chan]) chn_setdir(d->aplay[chan], PCMDIR_PLAY);
80 		if (d->arec[chan]) chn_setdir(d->arec[chan], PCMDIR_REC);
81 	}
82 }
83 
84 int
85 dsp_open(snddev_info *d, int chan, int oflags, int devtype)
86 {
87 	pcm_channel *rdch = NULL, *wrch = NULL;
88 	u_int32_t fmt;
89 
90 	if (chan >= d->chancount) return ENODEV;
91 	if (d->aplay[chan] || d->arec[chan]) return EBUSY;
92 	if (oflags & FREAD) {
93 		rdch = allocchn(d, PCMDIR_REC);
94 		if (!rdch) return EBUSY;
95 	}
96 	if (oflags & FWRITE) {
97 		wrch = allocchn(d, PCMDIR_PLAY);
98 		if (!wrch) {
99 			if (rdch) rdch->flags &= ~CHN_F_BUSY;
100 			return EBUSY;
101 		}
102 	}
103 	d->aplay[chan] = wrch;
104 	d->arec[chan] = rdch;
105 	switch (devtype) {
106 	case SND_DEV_DSP16:
107 		fmt = AFMT_S16_LE;
108 		break;
109 
110 	case SND_DEV_DSP:
111 		fmt = AFMT_U8;
112 		break;
113 
114 	case SND_DEV_AUDIO:
115 		fmt = AFMT_MU_LAW;
116 		break;
117 
118 	case SND_DEV_NORESET:
119 		fmt = 0;
120 		break;
121 
122 	default:
123 		return ENXIO;
124 	}
125 
126 	if (rdch) {
127 	        chn_reset(rdch);
128 		if (oflags & O_NONBLOCK) rdch->flags |= CHN_F_NBIO;
129 		if (fmt) {
130 			rdch->volume = (100 << 8) | 100;
131 			rdch->format = fmt;
132 			rdch->speed = DSP_DEFAULT_SPEED;
133 			rdch->blocksize = 2048;
134 		}
135 	}
136 	if (wrch) {
137 	        chn_reset(wrch);
138 		if (oflags & O_NONBLOCK) wrch->flags |= CHN_F_NBIO;
139 		if (fmt) {
140 			wrch->volume = (100 << 8) | 100;
141 			wrch->format = fmt;
142 			wrch->speed = DSP_DEFAULT_SPEED;
143 			wrch->blocksize = 2048;
144 		}
145 	}
146 	return 0;
147 }
148 
149 int
150 dsp_close(snddev_info *d, int chan, int devtype)
151 {
152 	pcm_channel *rdch, *wrch;
153 
154 	d->flags &= ~SD_F_TRANSIENT;
155 	rdch = d->arec[chan];
156 	wrch = d->aplay[chan];
157 
158 	if (rdch) {
159 		chn_abort(rdch);
160 		rdch->flags &= ~(CHN_F_BUSY | CHN_F_RUNNING | CHN_F_MAPPED);
161 	}
162 	if (wrch) wrch->flags &= ~(CHN_F_BUSY | CHN_F_RUNNING | CHN_F_MAPPED);
163 	d->aplay[chan] = NULL;
164 	d->arec[chan] = NULL;
165 	return 0;
166 }
167 
168 int
169 dsp_read(snddev_info *d, int chan, struct uio *buf, int flag)
170 {
171 	pcm_channel *rdch, *wrch;
172 
173 	if (!(d->flags & SD_F_PRIO_SET)) d->flags |= SD_F_PRIO_RD;
174 	if (!(d->flags & SD_F_DIR_SET)) setchns(d, chan);
175 	getchns(d, chan, &rdch, &wrch);
176 	if (!rdch || !(rdch->flags & CHN_F_BUSY))
177 		panic("dsp_read: non%s channel", rdch? "busy" : "existant");
178 	if (rdch->flags & CHN_F_MAPPED) return EINVAL;
179 	if (!(rdch->flags & CHN_F_RUNNING)) {
180 		rdch->flags |= CHN_F_RUNNING;
181 		chn_reinit(rdch);
182 	}
183 	return chn_read(rdch, buf);
184 }
185 
186 int
187 dsp_write(snddev_info *d, int chan, struct uio *buf, int flag)
188 {
189 	pcm_channel *rdch, *wrch;
190 
191 	if (!(d->flags & SD_F_PRIO_SET)) d->flags |= SD_F_PRIO_WR;
192 	if (!(d->flags & SD_F_DIR_SET)) setchns(d, chan);
193 	getchns(d, chan, &rdch, &wrch);
194 	if (!wrch || !(wrch->flags & CHN_F_BUSY))
195 		panic("dsp_write: non%s channel", wrch? "busy" : "existant");
196 	if (wrch->flags & CHN_F_MAPPED) return EINVAL;
197 	if (!(wrch->flags & CHN_F_RUNNING)) {
198 		wrch->flags |= CHN_F_RUNNING;
199 		chn_reinit(wrch);
200 	}
201 	return chn_write(wrch, buf);
202 }
203 
204 int
205 dsp_ioctl(snddev_info *d, int chan, u_long cmd, caddr_t arg)
206 {
207     	int ret = 0, *arg_i = (int *)arg;
208     	u_long s;
209     	pcm_channel *wrch = NULL, *rdch = NULL;
210 
211 	rdch = d->arec[chan];
212 	wrch = d->aplay[chan];
213 
214     	/*
215      	 * all routines are called with int. blocked. Make sure that
216      	 * ints are re-enabled when calling slow or blocking functions!
217      	 */
218     	s = spltty();
219     	switch(cmd) {
220 
221     	/*
222      	 * we start with the new ioctl interface.
223      	 */
224     	case AIONWRITE:	/* how many bytes can write ? */
225 		if (wrch && wrch->buffer.dl) chn_dmaupdate(wrch);
226 		*arg_i = wrch? wrch->buffer.fl : 0;
227 		break;
228 
229     	case AIOSSIZE:     /* set the current blocksize */
230 		{
231 	    		struct snd_size *p = (struct snd_size *)arg;
232 	    		splx(s);
233 	    		if (wrch) chn_setblocksize(wrch, p->play_size);
234 	    		if (rdch) chn_setblocksize(rdch, p->rec_size);
235 		}
236 		/* FALLTHROUGH */
237     	case AIOGSIZE:	/* get the current blocksize */
238 		{
239 	    		struct snd_size *p = (struct snd_size *)arg;
240 	    		if (wrch) p->play_size = wrch->blocksize;
241 	    		if (rdch) p->rec_size = rdch->blocksize;
242 		}
243 		break;
244 
245     	case AIOSFMT:
246 		{
247 	    		snd_chan_param *p = (snd_chan_param *)arg;
248 	    		splx(s);
249 	    		if (wrch) {
250 				chn_setformat(wrch, p->play_format);
251 				chn_setspeed(wrch, p->play_rate);
252 	    		}
253 	    		if (rdch) {
254 				chn_setformat(rdch, p->rec_format);
255 				chn_setspeed(rdch, p->rec_rate);
256 	    		}
257 		}
258 		/* FALLTHROUGH */
259 
260     	case AIOGFMT:
261 		{
262 	    		snd_chan_param *p = (snd_chan_param *)arg;
263 	    		p->play_rate = wrch? wrch->speed : 0;
264 	    		p->rec_rate = rdch? rdch->speed : 0;
265 	    		p->play_format = wrch? wrch->format : 0;
266 	    		p->rec_format = rdch? rdch->format : 0;
267 		}
268 		break;
269 
270     	case AIOGCAP:     /* get capabilities */
271 		{
272 	    		snd_capabilities *p = (snd_capabilities *)arg;
273 			pcmchan_caps *pcaps = NULL, *rcaps = NULL;
274 			if (rdch) rcaps = chn_getcaps(rdch);
275 			if (wrch) pcaps = chn_getcaps(wrch);
276 	    		p->rate_min = max(rcaps? rcaps->minspeed : 0,
277 	                      		  pcaps? pcaps->minspeed : 0);
278 	    		p->rate_max = min(rcaps? rcaps->maxspeed : 1000000,
279 	                      		  pcaps? pcaps->maxspeed : 1000000);
280 	    		p->bufsize = min(rdch? rdch->buffer.bufsize : 1000000,
281 	                     		 wrch? wrch->buffer.bufsize : 1000000);
282 			/* XXX bad on sb16 */
283 	    		p->formats = (rcaps? rcaps->formats : 0xffffffff) &
284 			 	     (pcaps? pcaps->formats : 0xffffffff);
285 	    		p->mixers = 1; /* default: one mixer */
286 	    		p->inputs = d->mixer.devs;
287 	    		p->left = p->right = 100;
288 		}
289 		break;
290 
291     	case AIOSTOP:
292 		if (*arg_i == AIOSYNC_PLAY && wrch) *arg_i = chn_abort(wrch);
293 		else if (*arg_i == AIOSYNC_CAPTURE && rdch) *arg_i = chn_abort(rdch);
294 		else {
295 		    	splx(s);
296 	   	 	printf("AIOSTOP: bad channel 0x%x\n", *arg_i);
297 	    		*arg_i = 0;
298 		}
299 		break;
300 
301     	case AIOSYNC:
302 		printf("AIOSYNC chan 0x%03lx pos %lu unimplemented\n",
303 	    		((snd_sync_parm *)arg)->chan, ((snd_sync_parm *)arg)->pos);
304 		break;
305 	/*
306 	 * here follow the standard ioctls (filio.h etc.)
307 	 */
308     	case FIONREAD: /* get # bytes to read */
309 		if (rdch && rdch->buffer.dl) chn_dmaupdate(rdch);
310 		*arg_i = rdch? rdch->buffer.rl : 0;
311 		break;
312 
313     	case FIOASYNC: /*set/clear async i/o */
314 		DEB( printf("FIOASYNC\n") ; )
315 		break;
316 
317     	case SNDCTL_DSP_NONBLOCK:
318     	case FIONBIO: /* set/clear non-blocking i/o */
319 		if (rdch) rdch->flags &= ~CHN_F_NBIO;
320 		if (wrch) wrch->flags &= ~CHN_F_NBIO;
321 		if (*arg_i) {
322 		    	if (rdch) rdch->flags |= CHN_F_NBIO;
323 		    	if (wrch) wrch->flags |= CHN_F_NBIO;
324 		}
325 		break;
326 
327     	/*
328 	 * Finally, here is the linux-compatible ioctl interface
329 	 */
330 #define THE_REAL_SNDCTL_DSP_GETBLKSIZE _IOWR('P', 4, int)
331     	case THE_REAL_SNDCTL_DSP_GETBLKSIZE:
332     	case SNDCTL_DSP_GETBLKSIZE:
333 		*arg_i = wrch? wrch->blocksize : 0; /* XXX rdch? */
334 		break ;
335 
336     	case SNDCTL_DSP_SETBLKSIZE:
337 		splx(s);
338 		if (wrch) chn_setblocksize(wrch, *arg_i);
339 		if (rdch) chn_setblocksize(rdch, *arg_i);
340 		break;
341 
342     	case SNDCTL_DSP_RESET:
343 		DEB(printf("dsp reset\n"));
344 		if (wrch) chn_abort(wrch);
345 		if (rdch) chn_abort(rdch);
346 		break;
347 
348     	case SNDCTL_DSP_SYNC:
349 		DEB(printf("dsp sync\n"));
350 		splx(s);
351 		if (wrch) chn_sync(wrch, wrch->buffer.bufsize - 4);
352 		break;
353 
354     	case SNDCTL_DSP_SPEED:
355 		splx(s);
356 		if (wrch) chn_setspeed(wrch, *arg_i);
357 		if (rdch) chn_setspeed(rdch, *arg_i);
358 		/* fallthru */
359 
360     	case SOUND_PCM_READ_RATE:
361 		*arg_i = wrch? wrch->speed : rdch->speed;
362 		break;
363 
364     	case SNDCTL_DSP_STEREO:
365 		splx(s);
366 		if (wrch) chn_setformat(wrch, (wrch->format & ~AFMT_STEREO) |
367 					((*arg_i)? AFMT_STEREO : 0));
368 		if (rdch) chn_setformat(rdch, (rdch->format & ~AFMT_STEREO) |
369 				        ((*arg_i)? AFMT_STEREO : 0));
370 		*arg_i = ((wrch? wrch->format : rdch->format) & AFMT_STEREO)? 1 : 0;
371 		break;
372 
373     	case SOUND_PCM_WRITE_CHANNELS:
374 		splx(s);
375 		if (wrch) chn_setformat(wrch, (wrch->format & ~AFMT_STEREO) |
376 					((*arg_i == 2)? AFMT_STEREO : 0));
377 		if (rdch) chn_setformat(rdch, (rdch->format & ~AFMT_STEREO) |
378 					((*arg_i == 2)? AFMT_STEREO : 0));
379 		/* fallthru */
380 
381     	case SOUND_PCM_READ_CHANNELS:
382 		*arg_i = ((wrch? wrch->format : rdch->format) & AFMT_STEREO)? 2 : 1;
383 		break;
384 
385     	case SNDCTL_DSP_GETFMTS:	/* returns a mask of supported fmts */
386 		*arg_i = wrch? chn_getcaps(wrch)->formats : chn_getcaps(rdch)->formats;
387 		break ;
388 
389     	case SNDCTL_DSP_SETFMT:	/* sets _one_ format */
390 		splx(s);
391 		if (wrch) chn_setformat(wrch, (*arg_i) | (wrch->format & AFMT_STEREO));
392 		if (rdch) chn_setformat(rdch, (*arg_i) | (rdch->format & AFMT_STEREO));
393 		*arg_i = (wrch? wrch->format: rdch->format) & ~AFMT_STEREO;
394 		break;
395 
396     	case SNDCTL_DSP_SUBDIVIDE:
397 		/* XXX watch out, this is RW! */
398 		DEB(printf("SNDCTL_DSP_SUBDIVIDE unimplemented\n");)
399 		break;
400 
401     	case SNDCTL_DSP_SETFRAGMENT:
402 		/* XXX watch out, this is RW! */
403 		DEB(printf("SNDCTL_DSP_SETFRAGMENT 0x%08x\n", *(int *)arg));
404 		{
405 		    	int bytes = 1 << min(*arg_i & 0xffff, 16);
406      		    	int count = (*arg_i >> 16) & 0xffff;
407 			pcm_channel *c = wrch? wrch : rdch;
408 	    		splx(s);
409 		    	if (rdch) chn_setblocksize(rdch, bytes);
410 		    	if (wrch) chn_setblocksize(wrch, bytes);
411 
412 			/* eg: 4dwave can only interrupt at buffer midpoint, so
413 			 * it will force blocksize == bufsize/2
414 			 */
415 	    		count = c->buffer.bufsize / c->blocksize;
416 	    		bytes = ffs(c->blocksize) - 1;
417 	    		*arg_i = (count << 16) | bytes;
418 		}
419 		break;
420 
421     	case SNDCTL_DSP_GETISPACE:
422 		/* return space available in the input queue */
423 		{
424 	    		audio_buf_info *a = (audio_buf_info *)arg;
425 	    		if (rdch) {
426 	        		snd_dbuf *b = &rdch->buffer;
427 	        		if (b->dl) chn_dmaupdate(rdch);
428 				a->bytes = b->fl;
429 	        		a->fragments = 1;
430 	        		a->fragstotal = b->bufsize / rdch->blocksize;
431 	        		a->fragsize = rdch->blocksize;
432 	    		}
433 		}
434 		break;
435 
436     	case SNDCTL_DSP_GETOSPACE:
437 		/* return space available in the output queue */
438 		{
439 	    		audio_buf_info *a = (audio_buf_info *)arg;
440 	    		if (wrch) {
441 	        		snd_dbuf *b = &wrch->buffer;
442 	        		if (b->dl) chn_dmaupdate(wrch);
443 				a->bytes = b->fl;
444 	        		a->fragments = 1;
445 	        		a->fragstotal = b->bufsize / wrch->blocksize;
446 	        		a->fragsize = wrch->blocksize;
447 	    		}
448 		}
449 		break;
450 
451     	case SNDCTL_DSP_GETIPTR:
452 		{
453 	    		count_info *a = (count_info *)arg;
454 	    		if (rdch) {
455     	        		snd_dbuf *b = &rdch->buffer;
456 	        		if (b->dl) chn_dmaupdate(rdch);
457 	        		a->bytes = b->total;
458 	        		a->blocks = (b->total - b->prev_total) / rdch->blocksize;
459 	        		a->ptr = b->fp;
460 	        		b->prev_total += a->blocks * rdch->blocksize;
461 	    		} else ret = EINVAL;
462 		}
463 		break;
464 
465     	case SNDCTL_DSP_GETOPTR:
466 		{
467 	    		count_info *a = (count_info *)arg;
468 	    		if (wrch) {
469     	        		snd_dbuf *b = &wrch->buffer;
470 	        		if (b->dl) chn_dmaupdate(wrch);
471 	        		a->bytes = b->total;
472 	        		a->blocks = (b->total - b->prev_total) / wrch->blocksize;
473 	        		a->ptr = b->rp;
474 	        		b->prev_total += a->blocks * wrch->blocksize;
475 	    		} else ret = EINVAL;
476 		}
477 		break;
478 
479     	case SNDCTL_DSP_GETCAPS:
480 		*arg_i = DSP_CAP_REALTIME | DSP_CAP_MMAP | DSP_CAP_TRIGGER;
481 		if (rdch && wrch && !(d->flags & SD_F_SIMPLEX))
482 			*arg_i |= DSP_CAP_DUPLEX;
483 		break;
484 
485     	case SOUND_PCM_READ_BITS:
486         	*arg_i = ((wrch? wrch->format : rdch->format) & AFMT_16BIT)? 16 : 8;
487 		break;
488 
489     	case SNDCTL_DSP_SETTRIGGER:
490 		if (rdch) {
491 			rdch->flags &= ~CHN_F_TRIGGERED;
492 		    	if (*arg_i & PCM_ENABLE_INPUT)
493 				rdch->flags |= CHN_F_TRIGGERED;
494 			chn_intr(rdch);
495 		}
496 		if (wrch) {
497 			wrch->flags &= ~CHN_F_TRIGGERED;
498 		    	if (*arg_i & PCM_ENABLE_OUTPUT)
499 				wrch->flags |= CHN_F_TRIGGERED;
500 			chn_intr(wrch);
501 		}
502 		break;
503 
504     	case SNDCTL_DSP_GETTRIGGER:
505 		*arg_i = 0;
506 		if (wrch && wrch->flags & CHN_F_TRIGGERED)
507 			*arg_i |= PCM_ENABLE_OUTPUT;
508 		if (rdch && rdch->flags & CHN_F_TRIGGERED)
509 			*arg_i |= PCM_ENABLE_INPUT;
510 		break;
511 
512 		case SNDCTL_DSP_GETODELAY:
513 			if (wrch) {
514 				snd_dbuf *b = &wrch->buffer;
515 				if (b->dl)
516 					chn_dmaupdate(wrch);
517 				*arg = b->total;
518 			} else
519 				ret = EINVAL;
520 			break;
521 
522     	case SNDCTL_DSP_MAPINBUF:
523     	case SNDCTL_DSP_MAPOUTBUF:
524     	case SNDCTL_DSP_SETSYNCRO:
525 		/* undocumented */
526 
527     	case SNDCTL_DSP_POST:
528     	case SOUND_PCM_WRITE_FILTER:
529     	case SOUND_PCM_READ_FILTER:
530 		/* dunno what these do, don't sound important */
531     	default:
532 		DEB(printf("default ioctl snd%d fn 0x%08x fail\n", unit, cmd));
533 		ret = EINVAL;
534 		break;
535     	}
536     	splx(s);
537     	return ret;
538 }
539 
540 int
541 dsp_poll(snddev_info *d, int chan, int events, struct proc *p)
542 {
543 	int ret = 0, e;
544 	pcm_channel *wrch = NULL, *rdch = NULL;
545 
546 	getchns(d, chan, &rdch, &wrch);
547 	e = events & (POLLOUT | POLLWRNORM);
548 	if (wrch && e) ret |= chn_poll(wrch, e, p);
549 	e = events & (POLLIN | POLLRDNORM);
550 	if (rdch && e) ret |= chn_poll(rdch, e, p);
551 	return ret;
552 }
553 
554 int
555 dsp_mmap(snddev_info *d, int chan, vm_offset_t offset, int nprot)
556 {
557 	pcm_channel *wrch = NULL, *rdch = NULL, *c = NULL;
558 
559 	getchns(d, chan, &rdch, &wrch);
560 	/* XXX this is broken by line 204 of vm/device_pager.c, so force write buffer */
561 	if (1 || (wrch && (nprot & PROT_WRITE))) c = wrch;
562 	else if (rdch && (nprot & PROT_READ)) c = rdch;
563 	if (c) {
564 		c->flags |= CHN_F_MAPPED;
565 		return atop(vtophys(c->buffer.buf + offset));
566 	}
567 	return -1;
568 }
569 
570