ALSA: snd-usb: add support for bit-reversed byte formats
There is quite some confusion around the bit-ordering in DSD samples,
and no general agreement that defines whether hardware is supposed to
expect the oldest sample in the MSB or the LSB of a byte.
ALSA will hence set the rule that on the software API layer, bytes
always carry the oldest bit in the most significant bit of a byte, and
the driver has to translate that at runtime in order to match the
hardware layout.
This patch adds support for this by adding a boolean flag to the
audio format struct.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 4cd917c..9723f3c 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -16,6 +16,7 @@
#include <linux/init.h>
#include <linux/slab.h>
+#include <linux/bitrev.h>
#include <linux/ratelimit.h>
#include <linux/usb.h>
#include <linux/usb/audio.h>
@@ -1264,7 +1265,12 @@
} else {
/* stuff the DSD payload */
int idx = (src_idx + subs->dsd_dop.byte_idx - 1) % wrap;
- dst[dst_idx++] = src[idx];
+
+ if (subs->cur_audiofmt->dsd_bitrev)
+ dst[dst_idx++] = bitrev8(src[idx]);
+ else
+ dst[dst_idx++] = src[idx];
+
subs->hwptr_done++;
}
}
@@ -1330,6 +1336,17 @@
if (unlikely(subs->pcm_format == SNDRV_PCM_FORMAT_DSD_U16_LE &&
subs->cur_audiofmt->dsd_dop)) {
fill_playback_urb_dsd_dop(subs, urb, bytes);
+ } else if (unlikely(subs->pcm_format == SNDRV_PCM_FORMAT_DSD_U8 &&
+ subs->cur_audiofmt->dsd_bitrev)) {
+ /* bit-reverse the bytes */
+ u8 *buf = urb->transfer_buffer;
+ for (i = 0; i < bytes; i++) {
+ int idx = (subs->hwptr_done + i)
+ % (runtime->buffer_size * stride);
+ buf[i] = bitrev8(runtime->dma_area[idx]);
+ }
+
+ subs->hwptr_done += bytes;
} else {
/* usual PCM */
if (subs->hwptr_done + bytes > runtime->buffer_size * stride) {