bluetooth: add CVSD codec implementation

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/507>

src/modules/bluetooth/bt-codec-cvsd.c

@@ -0,0 +1,122 @@
+/***
+  This file is part of PulseAudio.
+
+  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 2.1 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, see <http://www.gnu.org/licenses/>.
+***/
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include "a2dp-codec-api.h"
+
+typedef struct codec_info {
+    pa_sample_spec sample_spec;
+} codec_info_t;
+
+static void *init(bool for_encoding, bool for_backchannel, const uint8_t *config_buffer, uint8_t config_size, pa_sample_spec *sample_spec, pa_core *core) {
+    codec_info_t *info;
+
+    info = pa_xnew0(codec_info_t, 1);
+
+    info->sample_spec.format = PA_SAMPLE_S16LE;
+    info->sample_spec.channels = 1;
+    info->sample_spec.rate = 8000;
+
+    *sample_spec = info->sample_spec;
+
+    return info;
+}
+
+static void deinit(void *codec_info) {
+    pa_xfree(codec_info);
+}
+
+static int reset(void *codec_info) {
+    return 0;
+}
+
+static size_t get_block_size(void *codec_info, size_t link_mtu) {
+    codec_info_t *info = (codec_info_t *) codec_info;
+    size_t block_size = link_mtu;
+
+    if (!pa_frame_aligned(block_size, &info->sample_spec)) {
+        pa_log_debug("Got invalid block size: %lu, rounding down", block_size);
+        block_size = pa_frame_align(block_size, &info->sample_spec);
+    }
+
+    return block_size;
+}
+
+static size_t get_encoded_block_size(void *codec_info, size_t input_size) {
+    codec_info_t *info = (codec_info_t *) codec_info;
+
+    /* input size should be aligned to sample spec */
+    pa_assert_fp(pa_frame_aligned(input_size, &info->sample_spec));
+
+    return input_size;
+}
+
+static size_t reduce_encoder_bitrate(void *codec_info, size_t write_link_mtu) {
+    return 0;
+}
+
+static size_t increase_encoder_bitrate(void *codec_info, size_t write_link_mtu) {
+    return 0;
+}
+
+static size_t encode_buffer(void *codec_info, uint32_t timestamp, const uint8_t *input_buffer, size_t input_size, uint8_t *output_buffer, size_t output_size, size_t *processed) {
+    pa_assert(input_size <= output_size);
+
+    memcpy(output_buffer, input_buffer, input_size);
+    *processed = input_size;
+
+    return input_size;
+}
+
+static size_t decode_buffer(void *codec_info, const uint8_t *input_buffer, size_t input_size, uint8_t *output_buffer, size_t output_size, size_t *processed) {
+    codec_info_t *info = (codec_info_t *) codec_info;
+
+    *processed = input_size;
+
+    /* In some rare occasions, we might receive packets of a very strange
+     * size. This could potentially be possible if the SCO packet was
+     * received partially over-the-air, or more probably due to hardware
+     * issues in our Bluetooth adapter. In these cases, in order to avoid
+     * an assertion failure due to unaligned data, just discard the whole
+     * packet */
+    if (!pa_frame_aligned(input_size, &info->sample_spec)) {
+        pa_log_warn("SCO packet received of unaligned size: %zu", input_size);
+        return 0;
+    }
+
+    memcpy(output_buffer, input_buffer, input_size);
+
+    return input_size;
+}
+
+/* dummy passthrough codec used with HSP/HFP CVSD */
+const pa_a2dp_codec pa_bt_codec_cvsd = {
+    .name = "CVSD",
+    .description = "CVSD",
+    .init = init,
+    .deinit = deinit,
+    .reset = reset,
+    .get_read_block_size = get_block_size,
+    .get_write_block_size = get_block_size,
+    .get_encoded_block_size = get_encoded_block_size,
+    .reduce_encoder_bitrate = reduce_encoder_bitrate,
+    .increase_encoder_bitrate = increase_encoder_bitrate,
+    .encode_buffer = encode_buffer,
+    .decode_buffer = decode_buffer,
+};