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* u_audio.c -- ALSA audio utilities for Gadget stack
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* Copyright (C) 2008 Bryan Wu <cooloney@kernel.org>
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* Copyright (C) 2008 Analog Devices, Inc
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* Enter bugs at http://blackfin.uclinux.org/
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* Licensed under the GPL-2 or later.
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/device.h>
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#include <linux/delay.h>
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#include <linux/ctype.h>
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#include <linux/random.h>
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#include <linux/syscalls.h>
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* This component encapsulates the ALSA devices for USB audio gadget
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#define FILE_PCM_PLAYBACK "/dev/snd/pcmC0D0p"
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#define FILE_PCM_CAPTURE "/dev/snd/pcmC0D0c"
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#define FILE_CONTROL "/dev/snd/controlC0"
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static char *fn_play = FILE_PCM_PLAYBACK;
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module_param(fn_play, charp, S_IRUGO);
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MODULE_PARM_DESC(fn_play, "Playback PCM device file name");
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static char *fn_cap = FILE_PCM_CAPTURE;
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module_param(fn_cap, charp, S_IRUGO);
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MODULE_PARM_DESC(fn_cap, "Capture PCM device file name");
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static char *fn_cntl = FILE_CONTROL;
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module_param(fn_cntl, charp, S_IRUGO);
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MODULE_PARM_DESC(fn_cntl, "Control device file name");
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/*-------------------------------------------------------------------------*/
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* Some ALSA internal helper functions
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static int snd_interval_refine_set(struct snd_interval *i, unsigned int val)
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struct snd_interval t;
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t.openmin = t.openmax = 0;
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return snd_interval_refine(i, &t);
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static int _snd_pcm_hw_param_set(struct snd_pcm_hw_params *params,
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snd_pcm_hw_param_t var, unsigned int val,
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if (hw_is_mask(var)) {
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struct snd_mask *m = hw_param_mask(params, var);
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if (val == 0 && dir < 0) {
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changed = snd_mask_refine_set(
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hw_param_mask(params, var), val);
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} else if (hw_is_interval(var)) {
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struct snd_interval *i = hw_param_interval(params, var);
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if (val == 0 && dir < 0) {
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changed = snd_interval_refine_set(i, val);
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struct snd_interval t;
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changed = snd_interval_refine(i, &t);
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params->cmask |= 1 << var;
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params->rmask |= 1 << var;
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/*-------------------------------------------------------------------------*/
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* Set default hardware params
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static int playback_default_hw_params(struct gaudio_snd_dev *snd)
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struct snd_pcm_substream *substream = snd->substream;
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struct snd_pcm_hw_params *params;
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snd_pcm_sframes_t result;
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* SNDRV_PCM_ACCESS_RW_INTERLEAVED,
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* SNDRV_PCM_FORMAT_S16_LE
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snd->access = SNDRV_PCM_ACCESS_RW_INTERLEAVED;
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snd->format = SNDRV_PCM_FORMAT_S16_LE;
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params = kzalloc(sizeof(*params), GFP_KERNEL);
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_snd_pcm_hw_params_any(params);
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_snd_pcm_hw_param_set(params, SNDRV_PCM_HW_PARAM_ACCESS,
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_snd_pcm_hw_param_set(params, SNDRV_PCM_HW_PARAM_FORMAT,
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_snd_pcm_hw_param_set(params, SNDRV_PCM_HW_PARAM_CHANNELS,
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_snd_pcm_hw_param_set(params, SNDRV_PCM_HW_PARAM_RATE,
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snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL);
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snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_HW_PARAMS, params);
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result = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_PREPARE, NULL);
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"Preparing sound card failed: %d\n", (int)result);
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/* Store the hardware parameters */
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snd->access = params_access(params);
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snd->format = params_format(params);
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snd->channels = params_channels(params);
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snd->rate = params_rate(params);
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"Hardware params: access %x, format %x, channels %d, rate %d\n",
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snd->access, snd->format, snd->channels, snd->rate);
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* Playback audio buffer data by ALSA PCM device
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static size_t u_audio_playback(struct gaudio *card, void *buf, size_t count)
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struct gaudio_snd_dev *snd = &card->playback;
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struct snd_pcm_substream *substream = snd->substream;
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struct snd_pcm_runtime *runtime = substream->runtime;
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snd_pcm_sframes_t frames;
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if (runtime->status->state == SNDRV_PCM_STATE_XRUN ||
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runtime->status->state == SNDRV_PCM_STATE_SUSPENDED) {
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result = snd_pcm_kernel_ioctl(substream,
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SNDRV_PCM_IOCTL_PREPARE, NULL);
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ERROR(card, "Preparing sound card failed: %d\n",
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frames = bytes_to_frames(runtime, count);
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result = snd_pcm_lib_write(snd->substream, buf, frames);
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if (result != frames) {
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ERROR(card, "Playback error: %d\n", (int)result);
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static int u_audio_get_playback_channels(struct gaudio *card)
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return card->playback.channels;
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static int u_audio_get_playback_rate(struct gaudio *card)
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return card->playback.rate;
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* Open ALSA PCM and control device files
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* Initial the PCM or control device
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static int gaudio_open_snd_dev(struct gaudio *card)
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struct snd_pcm_file *pcm_file;
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struct gaudio_snd_dev *snd;
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/* Open control device */
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snd = &card->control;
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snd->filp = filp_open(fn_cntl, O_RDWR, 0);
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if (IS_ERR(snd->filp)) {
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int ret = PTR_ERR(snd->filp);
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ERROR(card, "unable to open sound control device file: %s\n",
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/* Open PCM playback device and setup substream */
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snd = &card->playback;
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snd->filp = filp_open(fn_play, O_WRONLY, 0);
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if (IS_ERR(snd->filp)) {
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ERROR(card, "No such PCM playback device: %s\n", fn_play);
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pcm_file = snd->filp->private_data;
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snd->substream = pcm_file->substream;
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playback_default_hw_params(snd);
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/* Open PCM capture device and setup substream */
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snd = &card->capture;
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snd->filp = filp_open(fn_cap, O_RDONLY, 0);
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if (IS_ERR(snd->filp)) {
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ERROR(card, "No such PCM capture device: %s\n", fn_cap);
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snd->substream = NULL;
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pcm_file = snd->filp->private_data;
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snd->substream = pcm_file->substream;
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* Close ALSA PCM and control device files
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static int gaudio_close_snd_dev(struct gaudio *gau)
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struct gaudio_snd_dev *snd;
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/* Close control device */
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filp_close(snd->filp, current->files);
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/* Close PCM playback device and setup substream */
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snd = &gau->playback;
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filp_close(snd->filp, current->files);
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/* Close PCM capture device and setup substream */
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filp_close(snd->filp, current->files);
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static struct gaudio *the_card;
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* gaudio_setup - setup ALSA interface and preparing for USB transfer
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* This sets up PCM, mixer or MIDI ALSA devices fore USB gadget using.
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* Returns negative errno, or zero on success
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int __init gaudio_setup(struct gaudio *card)
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ret = gaudio_open_snd_dev(card);
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ERROR(card, "we need at least one control device\n");
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* gaudio_cleanup - remove ALSA device interface
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* This is called to free all resources allocated by @gaudio_setup().
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void gaudio_cleanup(void)
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gaudio_close_snd_dev(the_card);