[PATCH 4.14 30/34] ALSA: firewire-motu: fix construction of PCM frame for capture direction

Greg Kroah-Hartman
2019-03-18T09:35:36Z

From: Takashi Sakamoto <o-takashi@sakamocchi.jp>

commit f97a0944a72b26a2bece72516294e112a890f98a upstream.

In data blocks of common isochronous packet for MOTU devices, PCM
frames are multiplexed in a shape of '24 bit * 4 Audio Pack', described
in IEC 61883-6. The frames are not aligned to quadlet.

For capture PCM substream, ALSA firewire-motu driver constructs PCM
frames by reading data blocks byte-by-byte. However this operation
includes bug for lower byte of the PCM sample. This brings invalid
content of the PCM samples.

This commit fixes the bug.

Reported-by: Peter Sjöberg <autopeter@gmail.com>
Cc: <stable@vger.kernel.org> # v4.12+
Fixes: 4641c9394010 ("ALSA: firewire-motu: add MOTU specific protocol layer")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/firewire/motu/amdtp-motu.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/sound/firewire/motu/amdtp-motu.c
+++ b/sound/firewire/motu/amdtp-motu.c
@@ -136,7 +136,9 @@ static void read_pcm_s32(struct amdtp_st
byte = (u8 *)buffer + p->pcm_byte_offset;

for (c = 0; c < channels; ++c) {
- *dst = (byte[0] << 24) | (byte[1] << 16) | byte[2];
+ *dst = (byte[0] << 24) |
+ (byte[1] << 16) |
+ (byte[2] << 8);
byte += 3;
dst++;
}