really create glitch-free branch

git-svn-id: file:///home/lennart/svn/public/pulseaudio/branches/glitch-free@2120 fefdeb5f-60dc-0310-8127-8f9354f1896f

1 files changed, 799 insertions, 0 deletions

diff --git a/src/modules/alsa-util.c b/src/modules/alsa-util.c
new file mode 100644
index 00000000..6afec3bc
--- /dev/null
+++ b/src/modules/alsa-util.c
@@ -0,0 +1,799 @@
+/* $Id$ */
+
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2004-2006 Lennart Poettering
+  Copyright 2006 Pierre Ossman <ossman@cendio.se> for Cendio AB
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2 of the License,
+  or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <sys/types.h>
+#include <asoundlib.h>
+
+#include <pulse/sample.h>
+#include <pulse/xmalloc.h>
+
+#include <pulsecore/log.h>
+#include <pulsecore/macro.h>
+#include <pulsecore/core-util.h>
+
+#include "alsa-util.h"
+
+struct pa_alsa_fdlist {
+    int num_fds;
+    struct pollfd *fds;
+    /* This is a temporary buffer used to avoid lots of mallocs */
+    struct pollfd *work_fds;
+
+    snd_mixer_t *mixer;
+
+    pa_mainloop_api *m;
+    pa_defer_event *defer;
+    pa_io_event **ios;
+
+    int polled;
+
+    void (*cb)(void *userdata);
+    void *userdata;
+};
+
+static void io_cb(pa_mainloop_api*a, pa_io_event* e, PA_GCC_UNUSED int fd, pa_io_event_flags_t events, void *userdata) {
+
+    struct pa_alsa_fdlist *fdl = userdata;
+    int err, i;
+    unsigned short revents;
+
+    pa_assert(a);
+    pa_assert(fdl);
+    pa_assert(fdl->mixer);
+    pa_assert(fdl->fds);
+    pa_assert(fdl->work_fds);
+
+    if (fdl->polled)
+        return;
+
+    fdl->polled = 1;
+
+    memcpy(fdl->work_fds, fdl->fds, sizeof(struct pollfd) * fdl->num_fds);
+
+    for (i = 0;i < fdl->num_fds; i++) {
+        if (e == fdl->ios[i]) {
+            if (events & PA_IO_EVENT_INPUT)
+                fdl->work_fds[i].revents |= POLLIN;
+            if (events & PA_IO_EVENT_OUTPUT)
+                fdl->work_fds[i].revents |= POLLOUT;
+            if (events & PA_IO_EVENT_ERROR)
+                fdl->work_fds[i].revents |= POLLERR;
+            if (events & PA_IO_EVENT_HANGUP)
+                fdl->work_fds[i].revents |= POLLHUP;
+            break;
+        }
+    }
+
+    pa_assert(i != fdl->num_fds);
+
+    if ((err = snd_mixer_poll_descriptors_revents(fdl->mixer, fdl->work_fds, fdl->num_fds, &revents)) < 0) {
+        pa_log_error("Unable to get poll revent: %s", snd_strerror(err));
+        return;
+    }
+
+    a->defer_enable(fdl->defer, 1);
+
+    if (revents)
+        snd_mixer_handle_events(fdl->mixer);
+}
+
+static void defer_cb(pa_mainloop_api*a, PA_GCC_UNUSED pa_defer_event* e, void *userdata) {
+    struct pa_alsa_fdlist *fdl = userdata;
+    int num_fds, i, err;
+    struct pollfd *temp;
+
+    pa_assert(a);
+    pa_assert(fdl);
+    pa_assert(fdl->mixer);
+
+    a->defer_enable(fdl->defer, 0);
+
+    num_fds = snd_mixer_poll_descriptors_count(fdl->mixer);
+    pa_assert(num_fds > 0);
+
+    if (num_fds != fdl->num_fds) {
+        if (fdl->fds)
+            pa_xfree(fdl->fds);
+        if (fdl->work_fds)
+            pa_xfree(fdl->work_fds);
+        fdl->fds = pa_xnew0(struct pollfd, num_fds);
+        fdl->work_fds = pa_xnew(struct pollfd, num_fds);
+    }
+
+    memset(fdl->work_fds, 0, sizeof(struct pollfd) * num_fds);
+
+    if ((err = snd_mixer_poll_descriptors(fdl->mixer, fdl->work_fds, num_fds)) < 0) {
+        pa_log_error("Unable to get poll descriptors: %s", snd_strerror(err));
+        return;
+    }
+
+    fdl->polled = 0;
+
+    if (memcmp(fdl->fds, fdl->work_fds, sizeof(struct pollfd) * num_fds) == 0)
+        return;
+
+    if (fdl->ios) {
+        for (i = 0; i < fdl->num_fds; i++)
+            a->io_free(fdl->ios[i]);
+
+        if (num_fds != fdl->num_fds) {
+            pa_xfree(fdl->ios);
+            fdl->ios = NULL;
+        }
+    }
+
+    if (!fdl->ios)
+        fdl->ios = pa_xnew(pa_io_event*, num_fds);
+
+    /* Swap pointers */
+    temp = fdl->work_fds;
+    fdl->work_fds = fdl->fds;
+    fdl->fds = temp;
+
+    fdl->num_fds = num_fds;
+
+    for (i = 0;i < num_fds;i++)
+        fdl->ios[i] = a->io_new(a, fdl->fds[i].fd,
+            ((fdl->fds[i].events & POLLIN) ? PA_IO_EVENT_INPUT : 0) |
+            ((fdl->fds[i].events & POLLOUT) ? PA_IO_EVENT_OUTPUT : 0),
+            io_cb, fdl);
+}
+
+struct pa_alsa_fdlist *pa_alsa_fdlist_new(void) {
+    struct pa_alsa_fdlist *fdl;
+
+    fdl = pa_xnew0(struct pa_alsa_fdlist, 1);
+
+    fdl->num_fds = 0;
+    fdl->fds = NULL;
+    fdl->work_fds = NULL;
+    fdl->mixer = NULL;
+    fdl->m = NULL;
+    fdl->defer = NULL;
+    fdl->ios = NULL;
+    fdl->polled = 0;
+
+    return fdl;
+}
+
+void pa_alsa_fdlist_free(struct pa_alsa_fdlist *fdl) {
+    pa_assert(fdl);
+
+    if (fdl->defer) {
+        pa_assert(fdl->m);
+        fdl->m->defer_free(fdl->defer);
+    }
+
+    if (fdl->ios) {
+        int i;
+        pa_assert(fdl->m);
+        for (i = 0;i < fdl->num_fds;i++)
+            fdl->m->io_free(fdl->ios[i]);
+        pa_xfree(fdl->ios);
+    }
+
+    if (fdl->fds)
+        pa_xfree(fdl->fds);
+    if (fdl->work_fds)
+        pa_xfree(fdl->work_fds);
+
+    pa_xfree(fdl);
+}
+
+int pa_alsa_fdlist_set_mixer(struct pa_alsa_fdlist *fdl, snd_mixer_t *mixer_handle, pa_mainloop_api* m) {
+    pa_assert(fdl);
+    pa_assert(mixer_handle);
+    pa_assert(m);
+    pa_assert(!fdl->m);
+
+    fdl->mixer = mixer_handle;
+    fdl->m = m;
+    fdl->defer = m->defer_new(m, defer_cb, fdl);
+
+    return 0;
+}
+
+static int set_format(snd_pcm_t *pcm_handle, snd_pcm_hw_params_t *hwparams, pa_sample_format_t *f) {
+
+    static const snd_pcm_format_t format_trans[] = {
+        [PA_SAMPLE_U8] = SND_PCM_FORMAT_U8,
+        [PA_SAMPLE_ALAW] = SND_PCM_FORMAT_A_LAW,
+        [PA_SAMPLE_ULAW] = SND_PCM_FORMAT_MU_LAW,
+        [PA_SAMPLE_S16LE] = SND_PCM_FORMAT_S16_LE,
+        [PA_SAMPLE_S16BE] = SND_PCM_FORMAT_S16_BE,
+        [PA_SAMPLE_FLOAT32LE] = SND_PCM_FORMAT_FLOAT_LE,
+        [PA_SAMPLE_FLOAT32BE] = SND_PCM_FORMAT_FLOAT_BE,
+        [PA_SAMPLE_S32LE] = SND_PCM_FORMAT_S32_LE,
+        [PA_SAMPLE_S32BE] = SND_PCM_FORMAT_S32_BE,
+    };
+
+    static const pa_sample_format_t try_order[] = {
+        PA_SAMPLE_FLOAT32NE,
+        PA_SAMPLE_FLOAT32RE,
+        PA_SAMPLE_S32NE,
+        PA_SAMPLE_S32RE,
+        PA_SAMPLE_S16NE,
+        PA_SAMPLE_S16RE,
+        PA_SAMPLE_ALAW,
+        PA_SAMPLE_ULAW,
+        PA_SAMPLE_U8,
+        PA_SAMPLE_INVALID
+    };
+
+    int i, ret;
+
+    pa_assert(pcm_handle);
+    pa_assert(f);
+
+    if ((ret = snd_pcm_hw_params_set_format(pcm_handle, hwparams, format_trans[*f])) >= 0)
+        return ret;
+
+    if (*f == PA_SAMPLE_FLOAT32BE)
+        *f = PA_SAMPLE_FLOAT32LE;
+    else if (*f == PA_SAMPLE_FLOAT32LE)
+        *f = PA_SAMPLE_FLOAT32BE;
+    else if (*f == PA_SAMPLE_S16BE)
+        *f = PA_SAMPLE_S16LE;
+    else if (*f == PA_SAMPLE_S16LE)
+        *f = PA_SAMPLE_S16BE;
+    else if (*f == PA_SAMPLE_S32BE)
+        *f = PA_SAMPLE_S32LE;
+    else if (*f == PA_SAMPLE_S32LE)
+        *f = PA_SAMPLE_S32BE;
+    else
+        goto try_auto;
+
+    if ((ret = snd_pcm_hw_params_set_format(pcm_handle, hwparams, format_trans[*f])) >= 0)
+        return ret;
+
+try_auto:
+
+    for (i = 0; try_order[i] != PA_SAMPLE_INVALID; i++) {
+        *f = try_order[i];
+
+        if ((ret = snd_pcm_hw_params_set_format(pcm_handle, hwparams, format_trans[*f])) >= 0)
+            return ret;
+    }
+
+    return -1;
+}
+
+/* Set the hardware parameters of the given ALSA device. Returns the
+ * selected fragment settings in *period and *period_size */
+int pa_alsa_set_hw_params(
+        snd_pcm_t *pcm_handle,
+        pa_sample_spec *ss,
+        uint32_t *periods,
+        snd_pcm_uframes_t *period_size,
+        pa_bool_t *use_mmap,
+        pa_bool_t require_exact_channel_number) {
+
+    int ret = -1;
+    snd_pcm_uframes_t buffer_size;
+    unsigned int r = ss->rate;
+    unsigned int c = ss->channels;
+    pa_sample_format_t f = ss->format;
+    snd_pcm_hw_params_t *hwparams;
+    pa_bool_t _use_mmap = use_mmap && *use_mmap;
+
+    pa_assert(pcm_handle);
+    pa_assert(ss);
+    pa_assert(periods);
+    pa_assert(period_size);
+
+    snd_pcm_hw_params_alloca(&hwparams);
+
+    buffer_size = *periods * *period_size;
+
+    if ((ret = snd_pcm_hw_params_any(pcm_handle, hwparams)) < 0)
+        goto finish;
+
+    if ((ret = snd_pcm_hw_params_set_rate_resample(pcm_handle, hwparams, 0)) < 0)
+        goto finish;
+
+    if (_use_mmap) {
+        if ((ret = snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_MMAP_INTERLEAVED)) < 0) {
+
+            /* mmap() didn't work, fall back to interleaved */
+
+            if ((ret = snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0)
+                goto finish;
+
+            _use_mmap = FALSE;
+        }
+
+    } else if ((ret = snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0)
+        goto finish;
+
+    if ((ret = set_format(pcm_handle, hwparams, &f)) < 0)
+        goto finish;
+
+    if ((ret = snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &r, NULL)) < 0)
+        goto finish;
+
+    if (require_exact_channel_number) {
+        if ((ret = snd_pcm_hw_params_set_channels(pcm_handle, hwparams, c)) < 0)
+            goto finish;
+    } else {
+        if ((ret = snd_pcm_hw_params_set_channels_near(pcm_handle, hwparams, &c)) < 0)
+            goto finish;
+    }
+
+    if ((*period_size > 0 && (ret = snd_pcm_hw_params_set_period_size_near(pcm_handle, hwparams, period_size, NULL)) < 0) ||
+        (*periods > 0 && (ret = snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, &buffer_size)) < 0))
+        goto finish;
+
+    if  ((ret = snd_pcm_hw_params(pcm_handle, hwparams)) < 0)
+        goto finish;
+
+    if (ss->rate != r)
+        pa_log_warn("Device %s doesn't support %u Hz, changed to %u Hz.", snd_pcm_name(pcm_handle), ss->rate, r);
+
+    if (ss->channels != c)
+        pa_log_warn("Device %s doesn't support %u channels, changed to %u.", snd_pcm_name(pcm_handle), ss->channels, c);
+
+    if (ss->format != f)
+        pa_log_warn("Device %s doesn't support sample format %s, changed to %s.", snd_pcm_name(pcm_handle), pa_sample_format_to_string(ss->format), pa_sample_format_to_string(f));
+
+    if ((ret = snd_pcm_prepare(pcm_handle)) < 0)
+        goto finish;
+
+    if ((ret = snd_pcm_hw_params_get_buffer_size(hwparams, &buffer_size)) < 0 ||
+        (ret = snd_pcm_hw_params_get_period_size(hwparams, period_size, NULL)) < 0)
+        goto finish;
+
+    /* If the sample rate deviates too much, we need to resample */
+    if (r < ss->rate*.95 || r > ss->rate*1.05)
+        ss->rate = r;
+    ss->channels = c;
+    ss->format = f;
+
+    pa_assert(buffer_size > 0);
+    pa_assert(*period_size > 0);
+    *periods = buffer_size / *period_size;
+    pa_assert(*periods > 0);
+
+    if (use_mmap)
+        *use_mmap = _use_mmap;
+
+    ret = 0;
+
+finish:
+
+    return ret;
+}
+
+int pa_alsa_set_sw_params(snd_pcm_t *pcm) {
+    snd_pcm_sw_params_t *swparams;
+    int err;
+
+    pa_assert(pcm);
+
+    snd_pcm_sw_params_alloca(&swparams);
+
+    if ((err = snd_pcm_sw_params_current(pcm, swparams) < 0)) {
+        pa_log_warn("Unable to determine current swparams: %s\n", snd_strerror(err));
+        return err;
+    }
+
+    if ((err = snd_pcm_sw_params_set_stop_threshold(pcm, swparams, (snd_pcm_uframes_t) -1)) < 0) {
+        pa_log_warn("Unable to set stop threshold: %s\n", snd_strerror(err));
+        return err;
+    }
+
+    if ((err = snd_pcm_sw_params_set_start_threshold(pcm, swparams, (snd_pcm_uframes_t) -1)) < 0) {
+        pa_log_warn("Unable to set start threshold: %s\n", snd_strerror(err));
+        return err;
+    }
+
+    if ((err = snd_pcm_sw_params(pcm, swparams)) < 0) {
+        pa_log_warn("Unable to set sw params: %s\n", snd_strerror(err));
+        return err;
+    }
+
+    return 0;
+}
+
+struct device_info {
+    pa_channel_map map;
+    const char *name;
+};
+
+static const struct device_info device_table[] = {
+    {{ 2, { PA_CHANNEL_POSITION_LEFT, PA_CHANNEL_POSITION_RIGHT } }, "front" },
+
+    {{ 4, { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+            PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT }}, "surround40" },
+
+    {{ 5, { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+            PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT,
+            PA_CHANNEL_POSITION_LFE }}, "surround41" },
+
+    {{ 5, { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+            PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT,
+            PA_CHANNEL_POSITION_CENTER }}, "surround50" },
+
+    {{ 6, { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+            PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT,
+            PA_CHANNEL_POSITION_CENTER, PA_CHANNEL_POSITION_LFE }}, "surround51" },
+
+    {{ 8, { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+            PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT,
+            PA_CHANNEL_POSITION_CENTER, PA_CHANNEL_POSITION_LFE,
+            PA_CHANNEL_POSITION_SIDE_LEFT, PA_CHANNEL_POSITION_SIDE_RIGHT }} , "surround71" },
+
+    {{ 0, { 0 }}, NULL }
+};
+
+static pa_bool_t channel_map_superset(const pa_channel_map *a, const pa_channel_map *b) {
+    pa_bool_t in_a[PA_CHANNEL_POSITION_MAX];
+    unsigned i;
+
+    pa_assert(a);
+    pa_assert(b);
+
+    memset(in_a, 0, sizeof(in_a));
+
+    for (i = 0; i < a->channels; i++)
+        in_a[a->map[i]] = TRUE;
+
+    for (i = 0; i < b->channels; i++)
+        if (!in_a[b->map[i]])
+            return FALSE;
+
+    return TRUE;
+}
+
+snd_pcm_t *pa_alsa_open_by_device_id(
+        const char *dev_id,
+        char **dev,
+        pa_sample_spec *ss,
+        pa_channel_map* map,
+        int mode,
+        uint32_t *nfrags,
+        snd_pcm_uframes_t *period_size,
+        pa_bool_t *use_mmap) {
+
+    int i;
+    int direction = 1;
+    int err;
+    char *d;
+    snd_pcm_t *pcm_handle;
+
+    pa_assert(dev_id);
+    pa_assert(dev);
+    pa_assert(ss);
+    pa_assert(map);
+    pa_assert(nfrags);
+    pa_assert(period_size);
+
+    /* First we try to find a device string with a superset of the
+     * requested channel map and open it without the plug: prefix. We
+     * iterate through our device table from top to bottom and take
+     * the first that matches. If we didn't find a working device that
+     * way, we iterate backwards, and check all devices that do not
+     * provide a superset of the requested channel map.*/
+
+    for (i = 0;; i += direction) {
+        pa_sample_spec try_ss;
+
+        if (i < 0) {
+            pa_assert(direction == -1);
+
+            /* OK, so we iterated backwards, and now are at the
+             * beginning of our list. */
+
+            break;
+
+        } else if (!device_table[i].name) {
+            pa_assert(direction == 1);
+
+            /* OK, so we are at the end of our list. at iterated
+             * forwards. */
+
+            i--;
+            direction = -1;
+        }
+
+        if ((direction > 0) == !channel_map_superset(&device_table[i].map, map))
+            continue;
+
+        d = pa_sprintf_malloc("%s:%s", device_table[i].name, dev_id);
+        pa_log_debug("Trying %s...", d);
+
+        if ((err = snd_pcm_open(&pcm_handle, d, mode, SND_PCM_NONBLOCK)) < 0) {
+            pa_log_info("Couldn't open PCM device %s: %s", d, snd_strerror(err));
+            pa_xfree(d);
+            continue;
+        }
+
+        try_ss.channels = device_table[i].map.channels;
+        try_ss.rate = ss->rate;
+        try_ss.format = ss->format;
+
+        if ((err = pa_alsa_set_hw_params(pcm_handle, &try_ss, nfrags, period_size, use_mmap, TRUE)) < 0) {
+            pa_log_info("PCM device %s refused our hw parameters: %s", d, snd_strerror(err));
+            pa_xfree(d);
+            snd_pcm_close(pcm_handle);
+            continue;
+        }
+
+        *ss = try_ss;
+        *map = device_table[i].map;
+        pa_assert(map->channels == ss->channels);
+        *dev = d;
+        return pcm_handle;
+    }
+
+    /* OK, we didn't find any good device, so let's try the raw hw: stuff */
+
+    d = pa_sprintf_malloc("hw:%s", dev_id);
+    pa_log_debug("Trying %s as last resort...", d);
+    pcm_handle = pa_alsa_open_by_device_string(d, dev, ss, map, mode, nfrags, period_size, use_mmap);
+    pa_xfree(d);
+
+    return pcm_handle;
+}
+
+snd_pcm_t *pa_alsa_open_by_device_string(
+        const char *device,
+        char **dev,
+        pa_sample_spec *ss,
+        pa_channel_map* map,
+        int mode,
+        uint32_t *nfrags,
+        snd_pcm_uframes_t *period_size,
+        pa_bool_t *use_mmap) {
+
+    int err;
+    char *d;
+    snd_pcm_t *pcm_handle;
+
+    pa_assert(device);
+    pa_assert(dev);
+    pa_assert(ss);
+    pa_assert(map);
+    pa_assert(nfrags);
+    pa_assert(period_size);
+
+    d = pa_xstrdup(device);
+
+    for (;;) {
+
+        if ((err = snd_pcm_open(&pcm_handle, d, mode, SND_PCM_NONBLOCK)) < 0) {
+            pa_log("Error opening PCM device %s: %s", d, snd_strerror(err));
+            pa_xfree(d);
+            return NULL;
+        }
+
+        if ((err = pa_alsa_set_hw_params(pcm_handle, ss, nfrags, period_size, use_mmap, FALSE)) < 0) {
+
+            if (err == -EPERM) {
+                /* Hmm, some hw is very exotic, so we retry with plug, if without it didn't work */
+
+                if (pa_startswith(d, "hw:")) {
+                    char *t = pa_sprintf_malloc("plughw:%s", d+3);
+                    pa_log_debug("Opening the device as '%s' didn't work, retrying with '%s'.", d, t);
+                    pa_xfree(d);
+                    d = t;
+
+                    snd_pcm_close(pcm_handle);
+                    continue;
+                }
+
+                pa_log("Failed to set hardware parameters on %s: %s", d, snd_strerror(err));
+                pa_xfree(d);
+                snd_pcm_close(pcm_handle);
+                return NULL;
+            }
+        }
+
+        *dev = d;
+
+        if (ss->channels != map->channels) {
+            pa_assert_se(pa_channel_map_init_auto(map, ss->channels, PA_CHANNEL_MAP_AUX));
+            pa_channel_map_init_auto(map, ss->channels, PA_CHANNEL_MAP_ALSA);
+        }
+
+        return pcm_handle;
+    }
+}
+
+int pa_alsa_prepare_mixer(snd_mixer_t *mixer, const char *dev) {
+    int err;
+
+    pa_assert(mixer);
+    pa_assert(dev);
+
+    if ((err = snd_mixer_attach(mixer, dev)) < 0) {
+        pa_log_info("Unable to attach to mixer %s: %s", dev, snd_strerror(err));
+        return -1;
+    }
+
+    if ((err = snd_mixer_selem_register(mixer, NULL, NULL)) < 0) {
+        pa_log_warn("Unable to register mixer: %s", snd_strerror(err));
+        return -1;
+    }
+
+    if ((err = snd_mixer_load(mixer)) < 0) {
+        pa_log_warn("Unable to load mixer: %s", snd_strerror(err));
+        return -1;
+    }
+
+    pa_log_info("Successfully attached to mixer '%s'", dev);
+
+    return 0;
+}
+
+snd_mixer_elem_t *pa_alsa_find_elem(snd_mixer_t *mixer, const char *name, const char *fallback) {
+    snd_mixer_elem_t *elem;
+    snd_mixer_selem_id_t *sid = NULL;
+
+    snd_mixer_selem_id_alloca(&sid);
+
+    pa_assert(mixer);
+    pa_assert(name);
+
+    snd_mixer_selem_id_set_name(sid, name);
+
+    if (!(elem = snd_mixer_find_selem(mixer, sid))) {
+        pa_log_info("Cannot find mixer control \"%s\".", snd_mixer_selem_id_get_name(sid));
+
+        if (fallback) {
+            snd_mixer_selem_id_set_name(sid, fallback);
+
+            if (!(elem = snd_mixer_find_selem(mixer, sid)))
+                pa_log_warn("Cannot find fallback mixer control \"%s\".", snd_mixer_selem_id_get_name(sid));
+        }
+    }
+
+    if (elem)
+        pa_log_info("Using mixer control \"%s\".", snd_mixer_selem_id_get_name(sid));
+
+    return elem;
+}
+
+static const snd_mixer_selem_channel_id_t alsa_channel_ids[PA_CHANNEL_POSITION_MAX] = {
+    [PA_CHANNEL_POSITION_MONO] = SND_MIXER_SCHN_MONO, /* The ALSA name is just an alias! */
+
+    [PA_CHANNEL_POSITION_FRONT_CENTER] = SND_MIXER_SCHN_FRONT_CENTER,
+    [PA_CHANNEL_POSITION_FRONT_LEFT] = SND_MIXER_SCHN_FRONT_LEFT,
+    [PA_CHANNEL_POSITION_FRONT_RIGHT] = SND_MIXER_SCHN_FRONT_RIGHT,
+
+    [PA_CHANNEL_POSITION_REAR_CENTER] = SND_MIXER_SCHN_REAR_CENTER,
+    [PA_CHANNEL_POSITION_REAR_LEFT] = SND_MIXER_SCHN_REAR_LEFT,
+    [PA_CHANNEL_POSITION_REAR_RIGHT] = SND_MIXER_SCHN_REAR_RIGHT,
+
+    [PA_CHANNEL_POSITION_LFE] = SND_MIXER_SCHN_WOOFER,
+
+    [PA_CHANNEL_POSITION_FRONT_LEFT_OF_CENTER] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_FRONT_RIGHT_OF_CENTER] = SND_MIXER_SCHN_UNKNOWN,
+
+    [PA_CHANNEL_POSITION_SIDE_LEFT] = SND_MIXER_SCHN_SIDE_LEFT,
+    [PA_CHANNEL_POSITION_SIDE_RIGHT] = SND_MIXER_SCHN_SIDE_RIGHT,
+
+    [PA_CHANNEL_POSITION_AUX0] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX1] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX2] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX3] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX4] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX5] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX6] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX7] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX8] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX9] =  SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX10] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX11] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX12] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX13] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX14] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX15] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX16] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX17] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX18] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX19] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX20] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX21] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX22] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX23] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX24] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX25] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX26] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX27] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX28] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX29] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX30] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_AUX31] = SND_MIXER_SCHN_UNKNOWN,
+
+    [PA_CHANNEL_POSITION_TOP_CENTER] = SND_MIXER_SCHN_UNKNOWN,
+
+    [PA_CHANNEL_POSITION_TOP_FRONT_CENTER] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_TOP_FRONT_LEFT] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_TOP_FRONT_RIGHT] = SND_MIXER_SCHN_UNKNOWN,
+
+    [PA_CHANNEL_POSITION_TOP_REAR_CENTER] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_TOP_REAR_LEFT] = SND_MIXER_SCHN_UNKNOWN,
+    [PA_CHANNEL_POSITION_TOP_REAR_RIGHT] = SND_MIXER_SCHN_UNKNOWN
+};
+
+
+int pa_alsa_calc_mixer_map(snd_mixer_elem_t *elem, const pa_channel_map *channel_map, snd_mixer_selem_channel_id_t mixer_map[], pa_bool_t playback) {
+    unsigned i;
+    pa_bool_t alsa_channel_used[SND_MIXER_SCHN_LAST];
+    pa_bool_t mono_used = FALSE;
+
+    pa_assert(elem);
+    pa_assert(channel_map);
+    pa_assert(mixer_map);
+
+    memset(&alsa_channel_used, 0, sizeof(alsa_channel_used));
+
+    if (channel_map->channels > 1 &&
+        ((playback && snd_mixer_selem_has_playback_volume_joined(elem)) ||
+         (!playback && snd_mixer_selem_has_capture_volume_joined(elem)))) {
+        pa_log_info("ALSA device lacks independant volume controls for each channel, falling back to software volume control.");
+        return -1;
+    }
+
+    for (i = 0; i < channel_map->channels; i++) {
+        snd_mixer_selem_channel_id_t id;
+        pa_bool_t is_mono;
+
+        is_mono = channel_map->map[i] == PA_CHANNEL_POSITION_MONO;
+        id = alsa_channel_ids[channel_map->map[i]];
+
+        if (!is_mono && id == SND_MIXER_SCHN_UNKNOWN) {
+            pa_log_info("Configured channel map contains channel '%s' that is unknown to the ALSA mixer. Falling back to software volume control.", pa_channel_position_to_string(channel_map->map[i]));
+            return -1;
+        }
+
+        if ((is_mono && mono_used) || (!is_mono && alsa_channel_used[id])) {
+            pa_log_info("Channel map has duplicate channel '%s', failling back to software volume control.", pa_channel_position_to_string(channel_map->map[i]));
+            return -1;
+        }
+
+        if ((playback && (!snd_mixer_selem_has_playback_channel(elem, id) || (is_mono && !snd_mixer_selem_is_playback_mono(elem)))) ||
+            (!playback && (!snd_mixer_selem_has_capture_channel(elem, id) || (is_mono && !snd_mixer_selem_is_capture_mono(elem))))) {
+
+            pa_log_info("ALSA device lacks separate volumes control for channel '%s', falling back to software volume control.", pa_channel_position_to_string(channel_map->map[i]));
+            return -1;
+        }
+
+        if (is_mono) {
+            mixer_map[i] = SND_MIXER_SCHN_MONO;
+            mono_used = TRUE;
+        } else {
+            mixer_map[i] = id;
+            alsa_channel_used[id] = TRUE;
+        }
+    }
+
+    pa_log_info("All %u channels can be mapped to mixer channels. Using hardware volume control.", channel_map->channels);
+
+    return 0;
+}