ALSA: usb-audio: Factor out DSD bitrev copy function

Just minor code refactoring.  Like DOP DSD code, it can be better in a
separate function for code readability.

Link: https://lore.kernel.org/r/20210601162457.4877-5-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 8ee45f2e8dceef11bb3f8ff5a8181ae5d346252e..e26d37365f0275282a3d3d9f458c153e4549b7b4 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1250,6 +1250,24 @@ static inline void fill_playback_urb_dsd_dop(struct snd_usb_substream *subs,
        urb_ctx_queue_advance(subs, urb, queued);
 }
 
+/* copy bit-reversed bytes onto transfer buffer */
+static void fill_playback_urb_dsd_bitrev(struct snd_usb_substream *subs,
+                                        struct urb *urb, unsigned int bytes)
+{
+       struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
+       const u8 *src = runtime->dma_area;
+       u8 *buf = urb->transfer_buffer;
+       int i, ofs = subs->hwptr_done;
+
+       for (i = 0; i < bytes; i++) {
+               *buf++ = bitrev8(src[ofs]);
+               if (++ofs >= subs->buffer_bytes)
+                       ofs = 0;
+       }
+
+       urb_ctx_queue_advance(subs, urb, bytes);
+}
+
 static void copy_to_urb(struct snd_usb_substream *subs, struct urb *urb,
                        int offset, int stride, unsigned int bytes)
 {
@@ -1360,15 +1378,7 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
                fill_playback_urb_dsd_dop(subs, urb, bytes);
        } else if (unlikely(ep->cur_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) % subs->buffer_bytes;
-
-                       buf[i] = bitrev8(runtime->dma_area[idx]);
-               }
-
-               urb_ctx_queue_advance(subs, urb, bytes);
+               fill_playback_urb_dsd_bitrev(subs, urb, bytes);
        } else {
                /* usual PCM */
                if (!subs->tx_length_quirk)