linux-kernel - [PATCH 1/2] ALSA: aloop: Add support for the non-interleaved access mode

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Date:   Wed, 27 Sep 2023 12:35:54 +0100
From:   Ivan Orlov <ivan.orlov0322@...il.com>
To:     perex@...ex.cz, tiwai@...e.com
Cc:     Ivan Orlov <ivan.orlov0322@...il.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] ALSA: aloop: Add support for the non-interleaved access mode

The current version of the loopback driver supports interleaved access
mode only. This patch introduces support for the non-interleaved
access mode.

When in the interleaved mode, the 'copy_play_buf' function copies data
from the playback to the capture buffer using one memcpy call. This call
copies samples for multiple, interleaved channels.

In the non-interleaved mode we have multiple channel buffers, so we have
to perform multiple memcpy calls to copy samples channel after channel.

Add new function called 'copy_play_buf_part_n', which copies a part of
each channel buffer from playback to capture. Modify the 'copy_play_buf'
to use the corresponding memory copy function(just memcpy /
copy_play_buf_part_n) depending on the access mode.

Signed-off-by: Ivan Orlov <ivan.orlov0322@...il.com>
---
 sound/drivers/aloop.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index a38e602b4fc6..ab116b1fed96 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -158,6 +158,9 @@ struct loopback_pcm {
 	unsigned long last_jiffies;
 	/* If jiffies timer is used */
 	struct timer_list timer;
+
+	/* size of per channel buffer in case of non-interleaved access */
+	unsigned int channel_buf_n;
 };
 
 static struct platform_device *devices[SNDRV_CARDS];
@@ -335,7 +338,8 @@ static int loopback_check_format(struct loopback_cable *cable, int stream)
 							substream->runtime;
 	check = runtime->format != cruntime->format ||
 		runtime->rate != cruntime->rate ||
-		runtime->channels != cruntime->channels;
+		runtime->channels != cruntime->channels ||
+		runtime->access != cruntime->access;
 	if (!check)
 		return 0;
 	if (stream == SNDRV_PCM_STREAM_CAPTURE) {
@@ -472,6 +476,7 @@ static int loopback_prepare(struct snd_pcm_substream *substream)
 
 	dpcm->buf_pos = 0;
 	dpcm->pcm_buffer_size = frames_to_bytes(runtime, runtime->buffer_size);
+	dpcm->channel_buf_n = dpcm->pcm_buffer_size / runtime->channels;
 	if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {
 		/* clear capture buffer */
 		dpcm->silent_size = dpcm->pcm_buffer_size;
@@ -522,6 +527,22 @@ static void clear_capture_buf(struct loopback_pcm *dpcm, unsigned int bytes)
 	}
 }
 
+static void copy_play_buf_part_n(struct loopback_pcm *play, struct loopback_pcm *capt,
+				 unsigned int size, unsigned int src_off, unsigned int dst_off)
+{
+	unsigned int channels = capt->substream->runtime->channels;
+	unsigned int size_p_ch = size / channels;
+	unsigned int src_off_ch = src_off / channels;
+	unsigned int dst_off_ch = dst_off / channels;
+	int i;
+
+	for (i = 0; i < channels; i++) {
+		memcpy(capt->substream->runtime->dma_area + capt->channel_buf_n * i + dst_off_ch,
+		       play->substream->runtime->dma_area + play->channel_buf_n * i + src_off_ch,
+		       size_p_ch);
+	}
+}
+
 static void copy_play_buf(struct loopback_pcm *play,
 			  struct loopback_pcm *capt,
 			  unsigned int bytes)
@@ -556,7 +577,11 @@ static void copy_play_buf(struct loopback_pcm *play,
 			size = play->pcm_buffer_size - src_off;
 		if (dst_off + size > capt->pcm_buffer_size)
 			size = capt->pcm_buffer_size - dst_off;
-		memcpy(dst + dst_off, src + src_off, size);
+		if (runtime->access == SNDRV_PCM_ACCESS_RW_NONINTERLEAVED ||
+		    runtime->access == SNDRV_PCM_ACCESS_MMAP_NONINTERLEAVED)
+			copy_play_buf_part_n(play, capt, size, src_off, dst_off);
+		else
+			memcpy(dst + dst_off, src + src_off, size);
 		capt->silent_size = 0;
 		bytes -= size;
 		if (!bytes)
@@ -878,7 +903,7 @@ static const struct snd_pcm_hardware loopback_pcm_hardware =
 {
 	.info =		(SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_MMAP |
 			 SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_PAUSE |
-			 SNDRV_PCM_INFO_RESUME),
+			 SNDRV_PCM_INFO_RESUME | SNDRV_PCM_INFO_NONINTERLEAVED),
 	.formats =	(SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S16_BE |
 			 SNDRV_PCM_FMTBIT_S24_LE | SNDRV_PCM_FMTBIT_S24_BE |
 			 SNDRV_PCM_FMTBIT_S24_3LE | SNDRV_PCM_FMTBIT_S24_3BE |
-- 
2.34.1