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authorDaniel Mack <zonque@gmail.com>2013-04-16 18:01:39 +0200
committerTakashi Iwai <tiwai@suse.de>2013-04-18 10:03:47 +0200
commit44dcbbb1cd615634c09d1bf31c124332795903a8 (patch)
treeef2b5642e14bcbb8fe082e1e60c83975556ac1aa /sound/usb/pcm.c
parentALSA: snd-usb: add support for DSD DOP stream transport (diff)
downloadlinux-44dcbbb1cd615634c09d1bf31c124332795903a8.tar.xz
linux-44dcbbb1cd615634c09d1bf31c124332795903a8.zip
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>
Diffstat (limited to 'sound/usb/pcm.c')
-rw-r--r--sound/usb/pcm.c19
1 files changed, 18 insertions, 1 deletions
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 4cd917cf058e..9723f3ceb155 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 @@ static inline void fill_playback_urb_dsd_dop(struct snd_usb_substream *subs,
} 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 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
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) {