cras_stream_apm: Skip processing on the main thread

process_reverse might be unexpectedlly called from the
main thread, if an iodev does not have start ops and
cras_iodev_fill_odev_zeros is used as a fallback.

This CL workarounds the assertion failure by doing nothing
in process_reverse() if it finds itself called out of the
audio thread. Skipping this data for the reverse apm stream
is OK because the zeros are expected to not be helpful for
echo cancellation anyway.

BUG=b:340129658
TEST=tast run dut12 audio.CrasMultiChannelCapture.\* audio.CrasAEC.\*

Change-Id: Ic3cdf3f0b6a007e39f97d01e5f3d823171461653
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/5534460
Commit-Queue: Li-Yu Yu <[email protected]>
Tested-by: [email protected] <[email protected]>
Reviewed-by: Yu-Hsuan Hsu <[email protected]>

Author: afq984

cras/src/server/cras_stream_apm.c

@@ -847,7 +847,12 @@ int cras_stream_apm_destroy(struct cras_stream_apm* stream) {
 static int process_reverse(struct float_buffer* fbuf,
                            unsigned int frame_rate,
                            const struct cras_iodev* echo_ref) {
-  struct cras_audio_ctx* actx = checked_audio_ctx();
+  // TODO(b/340138001): Switch back to checked_audio_ctx() after we stop
+  // calling this function in the main thread.
+  struct cras_audio_ctx* actx = get_audio_ctx_or_null();
+  if (!actx) {
+    return 0;
+  }
 
   struct active_apm* active;
   int ret;