Issue is in the mr_alsa_audio_pcm_playback_copy_internal() function of audio_driver.c that transfers the PCM samples from the ALSA buffer to the Ravenna buffer using the get_user() function.
In case of memory access mode the ALSA buffer can be directly accessed by the kernel and the samples must be copied.
mr_alsa_audio_pcm_playback_copy_internal() has been modified to handle the transfer of the ALSA buffer from user space (used with read/write access mode) and from kernel space (used by memory access mode).
The issue is common to all the platform but impacting ARM only.
Additional changes:
- changed type for dma_playback_offset and dma_capture_offset variables to uint32_t instead of atomic_t since the pointer callback mr_alsa_audio_pcm_pointer() is now atomic
- added variables to the mr_alsa_audio_chip scructure to decrease the number of calls to snd_pcm_lib_xxx() functions. These get assigned in the prepare callback mr_alsa_audio_pcm_prepare()
- changed mr_alsa_audio_get_playback_buffer_size_in_frames() to return configured size of Ravenna playback buffer (same as mr_alsa_audio_get_capture_buffer_size_in_frames())
- some rework of the existing patches
This fixes issue #20
