feeder_chain.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2008-2009 Ariff Abdullah <ariff@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
 
#ifdef HAVE_KERNEL_OPTION_HEADERS
#include "opt_snd.h"
#endif
 
#include <dev/sound/pcm/sound.h>
 
#include "feeder_if.h"
 
SND_DECLARE_FILE("$FreeBSD$");
 
/* chain state */
struct feeder_chain_state {
        uint32_t afmt;                          /* audio format */
        uint32_t rate;                          /* sampling rate */
        struct pcmchan_matrix *matrix;          /* matrix map */
};
 
/*
 * chain descriptor that will be passed around from the beginning until the
 * end of chain process.
 */
struct feeder_chain_desc {
        struct feeder_chain_state origin;       /* original state */
        struct feeder_chain_state current;      /* current state */
        struct feeder_chain_state target;       /* target state */
        struct pcm_feederdesc desc;             /* feeder descriptor */
        uint32_t afmt_ne;                       /* preferred native endian */
        int mode;                               /* chain mode */
        int use_eq;                             /* need EQ? */
        int use_matrix;                         /* need channel matrixing? */
        int use_volume;                         /* need softpcmvol? */
        int dummy;                              /* dummy passthrough */
        int expensive;                          /* possibly expensive */
};
 
#define FEEDER_CHAIN_LEAN               0
#define FEEDER_CHAIN_16                 1
#define FEEDER_CHAIN_32                 2
#define FEEDER_CHAIN_MULTI              3
#define FEEDER_CHAIN_FULLMULTI          4
#define FEEDER_CHAIN_LAST               5
 
#if defined(SND_FEEDER_FULL_MULTIFORMAT)
#define FEEDER_CHAIN_DEFAULT            FEEDER_CHAIN_FULLMULTI
#elif defined(SND_FEEDER_MULTIFORMAT)
#define FEEDER_CHAIN_DEFAULT            FEEDER_CHAIN_MULTI
#else
#define FEEDER_CHAIN_DEFAULT            FEEDER_CHAIN_LEAN
#endif
 
/*
 * List of preferred formats that might be required during
 * processing. It will be decided through snd_fmtbest().
 */
 
/* 'Lean' mode, signed 16 or 32 bit native endian. */
static uint32_t feeder_chain_formats_lean[] = {
        AFMT_S16_NE, AFMT_S32_NE,
        0
};
 
/* Force everything to signed 16 bit native endian. */
static uint32_t feeder_chain_formats_16[] = {
        AFMT_S16_NE,
        0
};
 
/* Force everything to signed 32 bit native endian. */
static uint32_t feeder_chain_formats_32[] = {
        AFMT_S32_NE,
        0
};
 
/* Multiple choices, all except 8 bit. */
static uint32_t feeder_chain_formats_multi[] = {
        AFMT_S16_LE, AFMT_S16_BE, AFMT_U16_LE, AFMT_U16_BE,
        AFMT_S24_LE, AFMT_S24_BE, AFMT_U24_LE, AFMT_U24_BE,
        AFMT_S32_LE, AFMT_S32_BE, AFMT_U32_LE, AFMT_U32_BE,
        0
};
 
/* Everything that is convertible. */
static uint32_t feeder_chain_formats_fullmulti[] = {
        AFMT_S8, AFMT_U8,
        AFMT_S16_LE, AFMT_S16_BE, AFMT_U16_LE, AFMT_U16_BE,
        AFMT_S24_LE, AFMT_S24_BE, AFMT_U24_LE, AFMT_U24_BE,
        AFMT_S32_LE, AFMT_S32_BE, AFMT_U32_LE, AFMT_U32_BE,
        0
};
 
static uint32_t *feeder_chain_formats[FEEDER_CHAIN_LAST] = {
        [FEEDER_CHAIN_LEAN]      = feeder_chain_formats_lean,
        [FEEDER_CHAIN_16]        = feeder_chain_formats_16,
        [FEEDER_CHAIN_32]        = feeder_chain_formats_32,
        [FEEDER_CHAIN_MULTI]     = feeder_chain_formats_multi,
        [FEEDER_CHAIN_FULLMULTI] = feeder_chain_formats_fullmulti
};
 
static int feeder_chain_mode = FEEDER_CHAIN_DEFAULT;
 
#if defined(_KERNEL) && defined(SND_DEBUG) && defined(SND_FEEDER_FULL_MULTIFORMAT)
SYSCTL_INT(_hw_snd, OID_AUTO, feeder_chain_mode, CTLFLAG_RWTUN,
    &feeder_chain_mode, 0,
    "feeder chain mode "
    "(0=lean, 1=16bit, 2=32bit, 3=multiformat, 4=fullmultiformat)");
#endif
 
/*
 * feeder_build_format(): Chain any format converter.
 */
static int
feeder_build_format(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        struct pcm_feederdesc *desc;
        int ret;
 
        desc = &(cdesc->desc);
        desc->type = FEEDER_FORMAT;
        desc->in = 0;
        desc->out = 0;
        desc->flags = 0;
 
        fc = feeder_getclass(desc);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_format\n", __func__);
                return (ENOTSUP);
        }
 
        desc->in = cdesc->current.afmt;
        desc->out = cdesc->target.afmt;
 
        ret = chn_addfeeder(c, fc, desc);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_format\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_FORMAT;
 
        cdesc->current.afmt = cdesc->target.afmt;
 
        return (0);
}
 
/*
 * feeder_build_formatne(): Chain format converter that suite best for native
 *                          endian format.
 */
static int
feeder_build_formatne(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_chain_state otarget;
        int ret;
 
        if (cdesc->afmt_ne == 0 ||
            AFMT_ENCODING(cdesc->current.afmt) == cdesc->afmt_ne)
                return (0);
 
        otarget = cdesc->target;
        cdesc->target = cdesc->current;
        cdesc->target.afmt = SND_FORMAT(cdesc->afmt_ne,
            cdesc->current.matrix->channels, cdesc->current.matrix->ext);
 
        ret = feeder_build_format(c, cdesc);
        if (ret != 0)
                return (ret);
 
        cdesc->target = otarget;
 
        return (0);
}
 
/*
 * feeder_build_rate(): Chain sample rate converter.
 */
static int
feeder_build_rate(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        struct pcm_feeder *f;
        struct pcm_feederdesc *desc;
        int ret;
 
        ret = feeder_build_formatne(c, cdesc);
        if (ret != 0)
                return (ret);
 
        desc = &(cdesc->desc);
        desc->type = FEEDER_RATE;
        desc->in = 0;
        desc->out = 0;
        desc->flags = 0;
 
        fc = feeder_getclass(desc);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_rate\n", __func__);
                return (ENOTSUP);
        }
 
        desc->in = cdesc->current.afmt;
        desc->out = desc->in;
 
        ret = chn_addfeeder(c, fc, desc);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_rate\n", __func__);
                return (ret);
        }
 
        f = c->feeder;
 
        /*
         * If in 'dummy' mode (possibly due to passthrough mode), set the
         * conversion quality to the lowest possible (should be fastest) since
         * listener won't be hearing anything. Theoretically we can just
         * disable it, but that will cause weird runtime behaviour:
         * application appear to play something that is either too fast or too
         * slow.
         */
        if (cdesc->dummy != 0) {
                ret = FEEDER_SET(f, FEEDRATE_QUALITY, 0);
                if (ret != 0) {
                        device_printf(c->dev,
                            "%s(): can't set resampling quality\n", __func__);
                        return (ret);
                }
        }
 
        ret = FEEDER_SET(f, FEEDRATE_SRC, cdesc->current.rate);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't set source rate\n", __func__);
                return (ret);
        }
 
        ret = FEEDER_SET(f, FEEDRATE_DST, cdesc->target.rate);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't set destination rate\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_RATE;
 
        cdesc->current.rate = cdesc->target.rate;
 
        return (0);
}
 
/*
 * feeder_build_matrix(): Chain channel matrixing converter.
 */
static int
feeder_build_matrix(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        struct pcm_feeder *f;
        struct pcm_feederdesc *desc;
        int ret;
 
        ret = feeder_build_formatne(c, cdesc);
        if (ret != 0)
                return (ret);
 
        desc = &(cdesc->desc);
        desc->type = FEEDER_MATRIX;
        desc->in = 0;
        desc->out = 0;
        desc->flags = 0;
 
        fc = feeder_getclass(desc);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_matrix\n", __func__);
                return (ENOTSUP);
        }
 
        desc->in = cdesc->current.afmt;
        desc->out = SND_FORMAT(cdesc->current.afmt,
            cdesc->target.matrix->channels, cdesc->target.matrix->ext);
 
        ret = chn_addfeeder(c, fc, desc);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_matrix\n", __func__);
                return (ret);
        }
 
        f = c->feeder;
        ret = feeder_matrix_setup(f, cdesc->current.matrix,
            cdesc->target.matrix);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): feeder_matrix_setup() failed\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_MATRIX;
 
        cdesc->current.afmt = desc->out;
        cdesc->current.matrix = cdesc->target.matrix;
        cdesc->use_matrix = 0;
 
        return (0);
}
 
/*
 * feeder_build_volume(): Chain soft volume.
 */
static int
feeder_build_volume(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        struct pcm_feeder *f;
        struct pcm_feederdesc *desc;
        int ret;
 
        ret = feeder_build_formatne(c, cdesc);
        if (ret != 0)
                return (ret);
 
        desc = &(cdesc->desc);
        desc->type = FEEDER_VOLUME;
        desc->in = 0;
        desc->out = 0;
        desc->flags = 0;
 
        fc = feeder_getclass(desc);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_volume\n", __func__);
                return (ENOTSUP);
        }
 
        desc->in = cdesc->current.afmt;
        desc->out = desc->in;
 
        ret = chn_addfeeder(c, fc, desc);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_volume\n", __func__);
                return (ret);
        }
 
        f = c->feeder;
 
        /*
         * If in 'dummy' mode (possibly due to passthrough mode), set BYPASS
         * mode since listener won't be hearing anything. Theoretically we can
         * just disable it, but that will confuse volume per channel mixer.
         */
        if (cdesc->dummy != 0) {
                ret = FEEDER_SET(f, FEEDVOLUME_STATE, FEEDVOLUME_BYPASS);
                if (ret != 0) {
                        device_printf(c->dev,
                            "%s(): can't set volume bypass\n", __func__);
                        return (ret);
                }
        }
 
        ret = feeder_volume_apply_matrix(f, cdesc->current.matrix);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): feeder_volume_apply_matrix() failed\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_VOLUME;
 
        cdesc->use_volume = 0;
 
        return (0);
}
 
/*
 * feeder_build_eq(): Chain parametric software equalizer.
 */
static int
feeder_build_eq(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        struct pcm_feeder *f;
        struct pcm_feederdesc *desc;
        int ret;
 
        ret = feeder_build_formatne(c, cdesc);
        if (ret != 0)
                return (ret);
 
        desc = &(cdesc->desc);
        desc->type = FEEDER_EQ;
        desc->in = 0;
        desc->out = 0;
        desc->flags = 0;
 
        fc = feeder_getclass(desc);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_eq\n", __func__);
                return (ENOTSUP);
        }
 
        desc->in = cdesc->current.afmt;
        desc->out = desc->in;
 
        ret = chn_addfeeder(c, fc, desc);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_eq\n", __func__);
                return (ret);
        }
 
        f = c->feeder;
 
        ret = FEEDER_SET(f, FEEDEQ_RATE, cdesc->current.rate);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't set rate on feeder_eq\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_EQ;
 
        cdesc->use_eq = 0;
 
        return (0);
}
 
/*
 * feeder_build_root(): Chain root feeder, the top, father of all.
 */
static int
feeder_build_root(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        int ret;
 
        fc = feeder_getclass(NULL);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_root\n", __func__);
                return (ENOTSUP);
        }
 
        ret = chn_addfeeder(c, fc, NULL);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_root\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_ROOT;
 
        c->feeder->desc->in = cdesc->current.afmt;
        c->feeder->desc->out = cdesc->current.afmt;
 
        return (0);
}
 
/*
 * feeder_build_mixer(): Chain software mixer for virtual channels.
 */
static int
feeder_build_mixer(struct pcm_channel *c, struct feeder_chain_desc *cdesc)
{
        struct feeder_class *fc;
        struct pcm_feederdesc *desc;
        int ret;
 
        desc = &(cdesc->desc);
        desc->type = FEEDER_MIXER;
        desc->in = 0;
        desc->out = 0;
        desc->flags = 0;
 
        fc = feeder_getclass(desc);
        if (fc == NULL) {
                device_printf(c->dev,
                    "%s(): can't find feeder_mixer\n", __func__);
                return (ENOTSUP);
        }
 
        desc->in = cdesc->current.afmt;
        desc->out = desc->in;
 
        ret = chn_addfeeder(c, fc, desc);
        if (ret != 0) {
                device_printf(c->dev,
                    "%s(): can't add feeder_mixer\n", __func__);
                return (ret);
        }
 
        c->feederflags |= 1 << FEEDER_MIXER;
 
        return (0);
}
 
/* Macrosses to ease our job doing stuffs later. */
#define FEEDER_BW(c, t)         ((c)->t.matrix->channels * (c)->t.rate)
 
#define FEEDRATE_UP(c)          ((c)->target.rate > (c)->current.rate)
#define FEEDRATE_DOWN(c)        ((c)->target.rate < (c)->current.rate)
#define FEEDRATE_REQUIRED(c)    (FEEDRATE_UP(c) || FEEDRATE_DOWN(c))
 
#define FEEDMATRIX_UP(c)        ((c)->target.matrix->channels >         \
                                 (c)->current.matrix->channels)
#define FEEDMATRIX_DOWN(c)      ((c)->target.matrix->channels <         \
                                 (c)->current.matrix->channels)
#define FEEDMATRIX_REQUIRED(c)  (FEEDMATRIX_UP(c) ||                    \
                                 FEEDMATRIX_DOWN(c) || (c)->use_matrix != 0)
 
#define FEEDFORMAT_REQUIRED(c)  (AFMT_ENCODING((c)->current.afmt) !=    \
                                 AFMT_ENCODING((c)->target.afmt))
 
#define FEEDVOLUME_REQUIRED(c)  ((c)->use_volume != 0)
 
#define FEEDEQ_VALIDRATE(c, t)  (feeder_eq_validrate((c)->t.rate) != 0)
#define FEEDEQ_ECONOMY(c)       (FEEDER_BW(c, current) < FEEDER_BW(c, target))
#define FEEDEQ_REQUIRED(c)      ((c)->use_eq != 0 &&                    \
                                 FEEDEQ_VALIDRATE(c, current))
 
#define FEEDFORMAT_NE_REQUIRED(c)                                       \
        ((c)->afmt_ne != AFMT_S32_NE &&                                 \
        (((c)->mode == FEEDER_CHAIN_16 &&                               \
        AFMT_ENCODING((c)->current.afmt) != AFMT_S16_NE) ||             \
        ((c)->mode == FEEDER_CHAIN_32 &&                                \
        AFMT_ENCODING((c)->current.afmt) != AFMT_S32_NE) ||             \
        (c)->mode == FEEDER_CHAIN_FULLMULTI ||                          \
        ((c)->mode == FEEDER_CHAIN_MULTI &&                             \
        ((c)->current.afmt & AFMT_8BIT)) ||                             \
        ((c)->mode == FEEDER_CHAIN_LEAN &&                              \
        !((c)->current.afmt & (AFMT_S16_NE | AFMT_S32_NE)))))
 
static void
feeder_default_matrix(struct pcmchan_matrix *m, uint32_t fmt, int id)
{
        int x;
 
        memset(m, 0, sizeof(*m));
 
        m->id = id;
        m->channels = AFMT_CHANNEL(fmt);
        m->ext = AFMT_EXTCHANNEL(fmt);
        for (x = 0; x != SND_CHN_T_MAX; x++)
                m->offset[x] = -1;
}
 
int
feeder_chain(struct pcm_channel *c)
{
        struct snddev_info *d;
        struct pcmchan_caps *caps;
        struct feeder_chain_desc cdesc;
        struct pcmchan_matrix *hwmatrix, *softmatrix;
        uint32_t hwfmt, softfmt;
        int ret;
 
        CHN_LOCKASSERT(c);
 
        /* Remove everything first. */
        while (chn_removefeeder(c) == 0)
                ;
 
        KASSERT(c->feeder == NULL, ("feeder chain not empty"));
 
        /* clear and populate chain descriptor. */
        bzero(&cdesc, sizeof(cdesc));
 
        switch (feeder_chain_mode) {
        case FEEDER_CHAIN_LEAN:
        case FEEDER_CHAIN_16:
        case FEEDER_CHAIN_32:
#if defined(SND_FEEDER_MULTIFORMAT) || defined(SND_FEEDER_FULL_MULTIFORMAT)
        case FEEDER_CHAIN_MULTI:
#endif
#if defined(SND_FEEDER_FULL_MULTIFORMAT)
        case FEEDER_CHAIN_FULLMULTI:
#endif
                break;
        default:
                feeder_chain_mode = FEEDER_CHAIN_DEFAULT;
                break;
        }
 
        cdesc.mode = feeder_chain_mode;
        cdesc.expensive = 1;    /* XXX faster.. */
 
#define VCHAN_PASSTHROUGH(c)    (((c)->flags & (CHN_F_VIRTUAL |         \
                                 CHN_F_PASSTHROUGH)) ==                 \
                                 (CHN_F_VIRTUAL | CHN_F_PASSTHROUGH))
 
        /* Get the best possible hardware format. */
        if (VCHAN_PASSTHROUGH(c))
                hwfmt = c->parentchannel->format;
        else {
                caps = chn_getcaps(c);
                if (caps == NULL || caps->fmtlist == NULL) {
                        device_printf(c->dev,
                            "%s(): failed to get channel caps\n", __func__);
                        return (ENODEV);
                }
 
                if ((c->format & AFMT_PASSTHROUGH) &&
                    !snd_fmtvalid(c->format, caps->fmtlist))
                        return (ENODEV);
 
                hwfmt = snd_fmtbest(c->format, caps->fmtlist);
                if (hwfmt == 0 || !snd_fmtvalid(hwfmt, caps->fmtlist)) {
                        device_printf(c->dev,
                            "%s(): invalid hardware format 0x%08x\n",
                            __func__, hwfmt);
                        {
                                int i;
                                for (i = 0; caps->fmtlist[i] != 0; i++)
                                        printf("0x%08x\n", caps->fmtlist[i]);
                                printf("Req: 0x%08x\n", c->format);
                        }
                        return (ENODEV);
                }
        }
 
        /*
         * The 'hardware' possibly have different interpretation of channel
         * matrixing, so get it first .....
         */
        hwmatrix = CHANNEL_GETMATRIX(c->methods, c->devinfo, hwfmt);
        if (hwmatrix == NULL) {
                /* setup a default matrix */
                hwmatrix = &c->matrix_scratch;
                feeder_default_matrix(hwmatrix, hwfmt,
                    SND_CHN_MATRIX_UNKNOWN);
        }
        /* ..... and rebuild hwfmt. */
        hwfmt = SND_FORMAT(hwfmt, hwmatrix->channels, hwmatrix->ext);
 
        /* Reset and rebuild default channel format/matrix map. */
        softfmt = c->format;
        softmatrix = &c->matrix;
        if (softmatrix->channels != AFMT_CHANNEL(softfmt) ||
            softmatrix->ext != AFMT_EXTCHANNEL(softfmt)) {
                softmatrix = feeder_matrix_format_map(softfmt);
                if (softmatrix == NULL) {
                        /* setup a default matrix */
                        softmatrix = &c->matrix;
                        feeder_default_matrix(softmatrix, softfmt,
                            SND_CHN_MATRIX_PCMCHANNEL);
                } else {
                        c->matrix = *softmatrix;
                        c->matrix.id = SND_CHN_MATRIX_PCMCHANNEL;
                }
        }
        softfmt = SND_FORMAT(softfmt, softmatrix->channels, softmatrix->ext);
        if (softfmt != c->format)
                device_printf(c->dev,
                    "%s(): WARNING: %s Soft format 0x%08x -> 0x%08x\n",
                    __func__, CHN_DIRSTR(c), c->format, softfmt);
 
        /*
         * PLAY and REC are opposite.
         */
        if (c->direction == PCMDIR_PLAY) {
                cdesc.origin.afmt    = softfmt;
                cdesc.origin.matrix  = softmatrix;
                cdesc.origin.rate    = c->speed;
                cdesc.target.afmt    = hwfmt;
                cdesc.target.matrix  = hwmatrix;
                cdesc.target.rate    = sndbuf_getspd(c->bufhard);
        } else {
                cdesc.origin.afmt    = hwfmt;
                cdesc.origin.matrix  = hwmatrix;
                cdesc.origin.rate    = sndbuf_getspd(c->bufhard);
                cdesc.target.afmt    = softfmt;
                cdesc.target.matrix  = softmatrix;
                cdesc.target.rate    = c->speed;
        }
 
        d = c->parentsnddev;
 
        /*
         * If channel is in bitperfect or passthrough mode, make it appear
         * that 'origin' and 'target' identical, skipping mostly chain
         * procedures.
         */
        if (CHN_BITPERFECT(c) || (c->format & AFMT_PASSTHROUGH)) {
                if (c->direction == PCMDIR_PLAY)
                        cdesc.origin = cdesc.target;
                else
                        cdesc.target = cdesc.origin;
                c->format = cdesc.target.afmt;
                c->speed  = cdesc.target.rate;
        } else {
                /* hwfmt is not convertible, so 'dummy' it. */
                if (hwfmt & AFMT_PASSTHROUGH)
                        cdesc.dummy = 1;
 
                if ((softfmt & AFMT_CONVERTIBLE) &&
                    (((d->flags & SD_F_VPC) && !(c->flags & CHN_F_HAS_VCHAN)) ||
                    (!(d->flags & SD_F_VPC) && (d->flags & SD_F_SOFTPCMVOL) &&
                    !(c->flags & CHN_F_VIRTUAL))))
                        cdesc.use_volume = 1;
 
                if (feeder_matrix_compare(cdesc.origin.matrix,
                    cdesc.target.matrix) != 0)
                        cdesc.use_matrix = 1;
 
                /* Soft EQ only applicable for PLAY. */
                if (cdesc.dummy == 0 &&
                    c->direction == PCMDIR_PLAY && (d->flags & SD_F_EQ) &&
                    (((d->flags & SD_F_EQ_PC) &&
                    !(c->flags & CHN_F_HAS_VCHAN)) ||
                    (!(d->flags & SD_F_EQ_PC) && !(c->flags & CHN_F_VIRTUAL))))
                        cdesc.use_eq = 1;
 
                if (FEEDFORMAT_NE_REQUIRED(&cdesc)) {
                        cdesc.afmt_ne =
                            (cdesc.dummy != 0) ?
                            snd_fmtbest(AFMT_ENCODING(softfmt),
                            feeder_chain_formats[cdesc.mode]) :
                            snd_fmtbest(AFMT_ENCODING(cdesc.target.afmt),
                            feeder_chain_formats[cdesc.mode]);
                        if (cdesc.afmt_ne == 0) {
                                device_printf(c->dev,
                                    "%s(): snd_fmtbest failed!\n", __func__);
                                cdesc.afmt_ne =
                                    (((cdesc.dummy != 0) ? softfmt :
                                    cdesc.target.afmt) &
                                    (AFMT_24BIT | AFMT_32BIT)) ?
                                    AFMT_S32_NE : AFMT_S16_NE;
                        }
                }
        }
 
        cdesc.current = cdesc.origin;
 
        /* Build everything. */
 
        c->feederflags = 0;
 
#define FEEDER_BUILD(t) do {                                            \
        ret = feeder_build_##t(c, &cdesc);                              \
        if (ret != 0)                                                   \
                return (ret);                                           \
        } while (0)
 
        if (!(c->flags & CHN_F_HAS_VCHAN) || c->direction == PCMDIR_REC)
                FEEDER_BUILD(root);
        else if (c->direction == PCMDIR_PLAY && (c->flags & CHN_F_HAS_VCHAN))
                FEEDER_BUILD(mixer);
        else
                return (ENOTSUP);
 
        /*
         * The basic idea is: The smaller the bandwidth, the cheaper the
         * conversion process, with following constraints:-
         *
         * 1) Almost all feeders work best in 16/32 native endian.
         * 2) Try to avoid 8bit feeders due to poor dynamic range.
         * 3) Avoid volume, format, matrix and rate in BITPERFECT or
         *    PASSTHROUGH mode.
         * 4) Try putting volume before EQ or rate. Should help to
         *    avoid/reduce possible clipping.
         * 5) EQ require specific, valid rate, unless it allow sloppy
         *    conversion.
         */
        if (FEEDMATRIX_UP(&cdesc)) {
                if (FEEDEQ_REQUIRED(&cdesc) &&
                    (!FEEDEQ_VALIDRATE(&cdesc, target) ||
                    (cdesc.expensive == 0 && FEEDEQ_ECONOMY(&cdesc))))
                        FEEDER_BUILD(eq);
                if (FEEDRATE_REQUIRED(&cdesc))
                        FEEDER_BUILD(rate);
                FEEDER_BUILD(matrix);
                if (FEEDVOLUME_REQUIRED(&cdesc))
                        FEEDER_BUILD(volume);
                if (FEEDEQ_REQUIRED(&cdesc))
                        FEEDER_BUILD(eq);
        } else if (FEEDMATRIX_DOWN(&cdesc)) {
                FEEDER_BUILD(matrix);
                if (FEEDVOLUME_REQUIRED(&cdesc))
                        FEEDER_BUILD(volume);
                if (FEEDEQ_REQUIRED(&cdesc) &&
                    (!FEEDEQ_VALIDRATE(&cdesc, target) ||
                    FEEDEQ_ECONOMY(&cdesc)))
                        FEEDER_BUILD(eq);
                if (FEEDRATE_REQUIRED(&cdesc))
                        FEEDER_BUILD(rate);
                if (FEEDEQ_REQUIRED(&cdesc))
                        FEEDER_BUILD(eq);
        } else {
                if (FEEDRATE_DOWN(&cdesc)) {
                        if (FEEDEQ_REQUIRED(&cdesc) &&
                            !FEEDEQ_VALIDRATE(&cdesc, target)) {
                                if (FEEDVOLUME_REQUIRED(&cdesc))
                                        FEEDER_BUILD(volume);
                                FEEDER_BUILD(eq);
                        }
                        FEEDER_BUILD(rate);
                }
                if (FEEDMATRIX_REQUIRED(&cdesc))
                        FEEDER_BUILD(matrix);
                if (FEEDVOLUME_REQUIRED(&cdesc))
                        FEEDER_BUILD(volume);
                if (FEEDRATE_UP(&cdesc)) {
                        if (FEEDEQ_REQUIRED(&cdesc) &&
                            !FEEDEQ_VALIDRATE(&cdesc, target))
                                FEEDER_BUILD(eq);
                        FEEDER_BUILD(rate);
                }
                if (FEEDEQ_REQUIRED(&cdesc))
                        FEEDER_BUILD(eq);
        }
 
        if (FEEDFORMAT_REQUIRED(&cdesc))
                FEEDER_BUILD(format);
 
        if (c->direction == PCMDIR_REC && (c->flags & CHN_F_HAS_VCHAN))
                FEEDER_BUILD(mixer);
 
        sndbuf_setfmt(c->bufsoft, c->format);
        sndbuf_setspd(c->bufsoft, c->speed);
 
        sndbuf_setfmt(c->bufhard, hwfmt);
 
        chn_syncstate(c);
 
        return (0);
}