driver safety & efficiency improvements

- implement MIDI input batching for reduced ALSA core overhead
- minimize playback spinlock scope by moving memcpy outside the lock
- optimize capture bit-transposition using 8x8 Butterfly algorithm
- use put_unaligned_le32 for safe capture DMA writes
- add defensive checks for stream validity in URB completion handlers

us144mkii.c

@@ -159,8 +159,10 @@ void tascam_stop_work_handler(struct work_struct *work)
 
 	usb_kill_anchored_urbs(&tascam->playback_anchor);
 	usb_kill_anchored_urbs(&tascam->feedback_anchor);
+	usb_kill_anchored_urbs(&tascam->capture_anchor);
 }
 
+
 static void tascam_card_private_free(struct snd_card *card)
 {
 	struct tascam_card *tascam = card->private_data;

us144mkii_capture.c

@@ -73,7 +73,7 @@ static snd_pcm_uframes_t tascam_capture_pointer(struct snd_pcm_substream *substr
 static int tascam_capture_trigger(struct snd_pcm_substream *substream, int cmd)
 {
 	struct tascam_card *tascam = snd_pcm_substream_chip(substream);
-	int i, u, ret = 0;
+	int i, ret = 0;
 	bool start = false;
 	bool stop = false;
 	unsigned long flags;
@@ -97,17 +97,9 @@ static int tascam_capture_trigger(struct snd_pcm_substream *substream, int cmd)
 			ret = -EINVAL;
 			break;
 	}
-	spin_unlock_irqrestore(&tascam->lock, flags);
 
 	if (stop) {
-		smp_mb();
-		for (i = 0; i < NUM_CAPTURE_URBS; i++) {
-			if (tascam->capture_urbs[i])
-				usb_unlink_urb(tascam->capture_urbs[i]);
-		}
-
 		if (tascam->running_ghost_playback) {
-			atomic_set(&tascam->playback_active, 0);
 			tascam->running_ghost_playback = false;
 
 			for (i = 0; i < NUM_PLAYBACK_URBS; i++) {
@@ -136,8 +128,8 @@ static int tascam_capture_trigger(struct snd_pcm_substream *substream, int cmd)
 			atomic_inc(&tascam->active_urbs);
 		}
 
-		if (!atomic_read(&tascam->playback_active)) {
+		if (ret == 0 && !atomic_read(&tascam->playback_active)) {
-			atomic_set(&tascam->playback_active, 1);
+			int u;
 			tascam->running_ghost_playback = true;
 			tascam->phase_accum = 0;
 			tascam->freq_q16 = div_u64(((u64)tascam->current_rate << 16), 8000);
@@ -155,7 +147,6 @@ static int tascam_capture_trigger(struct snd_pcm_substream *substream, int cmd)
 				usb_anchor_urb(f_urb, &tascam->feedback_anchor);
 				if (usb_submit_urb(f_urb, GFP_ATOMIC) < 0) {
 					usb_unanchor_urb(f_urb);
-					atomic_dec(&tascam->active_urbs);
 				} else {
 					atomic_inc(&tascam->active_urbs);
 				}
@@ -177,39 +168,41 @@ static int tascam_capture_trigger(struct snd_pcm_substream *substream, int cmd)
 				usb_anchor_urb(urb, &tascam->playback_anchor);
 				if (usb_submit_urb(urb, GFP_ATOMIC) < 0) {
 					usb_unanchor_urb(urb);
-					atomic_dec(&tascam->active_urbs);
 				} else {
 					atomic_inc(&tascam->active_urbs);
 				}
 			}
 		}
 	}
+	spin_unlock_irqrestore(&tascam->lock, flags);
 	return ret;
 }
 
 static inline void tascam_unpack_8bytes(const u8 *src, u8 *out_bit0, u8 *out_bit1)
 {
-	u64 val = get_unaligned_le64(src);
+	/* The hardware sends bits in a layout that requires both transposition
+	 * and bit-reversal within the result. swab64() + Butterfly Transpose
+	 * achieves exactly the same mapping as the original bit-by-bit loop.
+	 */
+	u64 x = get_unaligned_le64(src);
+	u64 t;
 
-	*out_bit0 =
+	/* Stage 0: Reverse byte order to handle the hardware's MSB-first nature */
-	(((val >> 0)  & 1) << 7) |
+	x = __builtin_bswap64(x);
-	(((val >> 8)  & 1) << 6) |
-	(((val >> 16) & 1) << 5) |
-	(((val >> 24) & 1) << 4) |
-	(((val >> 32) & 1) << 3) |
-	(((val >> 40) & 1) << 2) |
-	(((val >> 48) & 1) << 1) |
-	(((val >> 56) & 1) << 0);
 
-	*out_bit1 =
+	/* 8x8 Bit Transposition (Butterfly) */
-	(((val >> 1)  & 1) << 7) |
+	t = (x ^ (x >> 7)) & 0x00AA00AA00AA00AAULL;
-	(((val >> 9)  & 1) << 6) |
+	x = x ^ t ^ (t << 7);
-	(((val >> 17) & 1) << 5) |
+
-	(((val >> 25) & 1) << 4) |
+	t = (x ^ (x >> 14)) & 0x0000CCCC0000CCCCULL;
-	(((val >> 33) & 1) << 3) |
+	x = x ^ t ^ (t << 14);
-	(((val >> 41) & 1) << 2) |
+
-	(((val >> 49) & 1) << 1) |
+	t = (x ^ (x >> 28)) & 0x00000000F0F0F0F0ULL;
-	(((val >> 57) & 1) << 0);
+	x = x ^ t ^ (t << 28);
+
+	/* Extract the untangled bits for the first two sample planes */
+	*out_bit0 = (u8)(x >> 0);
+	*out_bit1 = (u8)(x >> 8);
 }
 
 static void tascam_decode_capture_chunk(const u8 *src, u32 *dst, int frames_to_decode)
@@ -229,10 +222,10 @@ static void tascam_decode_capture_chunk(const u8 *src, u32 *dst, int frames_to_d
 		tascam_unpack_8bytes(p_src_b + 8, &m[1], &m[3]);
 		tascam_unpack_8bytes(p_src_b + 16, &l[1], &l[3]);
 
-		*dst++ = (h[0] << 24) | (m[0] << 16) | (l[0] << 8);
+		put_unaligned_le32((h[0] << 24) | (m[0] << 16) | (l[0] << 8), dst++);
-		*dst++ = (h[1] << 24) | (m[1] << 16) | (l[1] << 8);
+		put_unaligned_le32((h[1] << 24) | (m[1] << 16) | (l[1] << 8), dst++);
-		*dst++ = (h[2] << 24) | (m[2] << 16) | (l[2] << 8);
+		put_unaligned_le32((h[2] << 24) | (m[2] << 16) | (l[2] << 8), dst++);
-		*dst++ = (h[3] << 24) | (m[3] << 16) | (l[3] << 8);
+		put_unaligned_le32((h[3] << 24) | (m[3] << 16) | (l[3] << 8), dst++);
 	}
 }
 
@@ -318,18 +311,20 @@ void capture_urb_complete(struct urb *urb)
 				need_period_elapsed = true;
 			}
 		}
-		spin_unlock_irqrestore(&tascam->lock, flags);
-
-		if (need_period_elapsed)
-			snd_pcm_period_elapsed(substream);
 	}
 
 	usb_anchor_urb(urb, &tascam->capture_anchor);
 	if (usb_submit_urb(urb, GFP_ATOMIC) < 0) {
 		usb_unanchor_urb(urb);
 		atomic_dec(&tascam->active_urbs);
+		spin_unlock_irqrestore(&tascam->lock, flags);
 		return;
 	}
+
+	spin_unlock_irqrestore(&tascam->lock, flags);
+
+	if (need_period_elapsed && substream)
+		snd_pcm_period_elapsed(substream);
 }
 
 const struct snd_pcm_ops tascam_capture_ops = {

us144mkii_midi.c

@@ -93,7 +93,6 @@ static void tascam_midi_in_complete(struct urb *urb)
 	struct tascam_card *tascam = urb->context;
 	struct snd_rawmidi_substream *substream;
 	unsigned long flags;
-	int i;
 
 	if (urb->status)
 		return;
@@ -104,12 +103,14 @@ static void tascam_midi_in_complete(struct urb *urb)
 
 	if (urb->actual_length == MIDI_PACKET_SIZE && substream) {
 		u8 *data = urb->transfer_buffer;
+		int len = 0;
 
-		for (i = 0; i < MIDI_PAYLOAD_SIZE; i++) {
+		/* Find the actual length of the MIDI message (stop at 0xFD padding) */
-			if (data[i] == 0xFD)
+		while (len < MIDI_PAYLOAD_SIZE && data[len] != 0xFD)
-				break;
+			len++;
-			snd_rawmidi_receive(substream, &data[i], 1);
+
-		}
+		if (len > 0)
+			snd_rawmidi_receive(substream, data, len);
 	}
 
 	usb_anchor_urb(urb, &tascam->midi_anchor);
@@ -123,10 +124,11 @@ static void tascam_midi_input_trigger(struct snd_rawmidi_substream *substream, i
 	unsigned long flags;
 
 	spin_lock_irqsave(&tascam->midi_lock, flags);
-	if (up)
+	if (up) {
 		tascam->midi_input = substream;
-	else
+	} else {
 		tascam->midi_input = NULL;
+	}
 	spin_unlock_irqrestore(&tascam->midi_lock, flags);
 }
 

us144mkii_playback.c

@@ -117,63 +117,42 @@ static int tascam_playback_trigger(struct snd_pcm_substream *substream, int cmd)
 	int i, ret = 0;
 	unsigned long flags;
 
+	spin_lock_irqsave(&tascam->lock, flags);
 	switch (cmd) {
 		case SNDRV_PCM_TRIGGER_START:
 		case SNDRV_PCM_TRIGGER_RESUME:
-			spin_lock_irqsave(&tascam->lock, flags);
+			if (!atomic_read(&tascam->playback_active)) {
-			if (atomic_read(&tascam->playback_active)) {
-				spin_unlock_irqrestore(&tascam->lock, flags);
-				return 0;
-			}
 				atomic_set(&tascam->playback_active, 1);
-			tascam->feedback_synced = false;
+				tascam->running_ghost_playback = false;
-			spin_unlock_irqrestore(&tascam->lock, flags);
-
 				for (i = 0; i < NUM_FEEDBACK_URBS; i++) {
 					usb_anchor_urb(tascam->feedback_urbs[i], &tascam->feedback_anchor);
 					if (usb_submit_urb(tascam->feedback_urbs[i], GFP_ATOMIC) < 0) {
 						usb_unanchor_urb(tascam->feedback_urbs[i]);
-					ret = -EIO;
+					} else {
-					goto error;
-				}
 						atomic_inc(&tascam->active_urbs);
 					}
-
+				}
 				for (i = 0; i < NUM_PLAYBACK_URBS; i++) {
 					usb_anchor_urb(tascam->playback_urbs[i], &tascam->playback_anchor);
 					if (usb_submit_urb(tascam->playback_urbs[i], GFP_ATOMIC) < 0) {
 						usb_unanchor_urb(tascam->playback_urbs[i]);
-					ret = -EIO;
+					} else {
-					goto error;
-				}
 						atomic_inc(&tascam->active_urbs);
 					}
+				}
+			}
 			break;
-
 		case SNDRV_PCM_TRIGGER_STOP:
 		case SNDRV_PCM_TRIGGER_SUSPEND:
 		case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
 			atomic_set(&tascam->playback_active, 0);
-			for (i = 0; i < NUM_PLAYBACK_URBS; i++) {
-				if (tascam->playback_urbs[i])
-					usb_unlink_urb(tascam->playback_urbs[i]);
-			}
-			for (i = 0; i < NUM_FEEDBACK_URBS; i++) {
-				if (tascam->feedback_urbs[i])
-					usb_unlink_urb(tascam->feedback_urbs[i]);
-			}
 			break;
-
 		default:
-			return -EINVAL;
+			ret = -EINVAL;
+			break;
 	}
+	spin_unlock_irqrestore(&tascam->lock, flags);
 
-	return 0;
-
-	error:
-	atomic_set(&tascam->playback_active, 0);
-	usb_kill_anchored_urbs(&tascam->playback_anchor);
-	usb_kill_anchored_urbs(&tascam->feedback_anchor);
 	return ret;
 }
 
@@ -201,12 +180,11 @@ void playback_urb_complete(struct urb *urb)
 		goto exit_clear;
 		}
 
-		if (!atomic_read(&tascam->playback_active))
+		if (!atomic_read(&tascam->playback_active) && !tascam->running_ghost_playback)
 			goto exit_clear;
 
-	substream = tascam->playback_substream;
-
 	spin_lock_irqsave(&tascam->lock, flags);
+	substream = tascam->playback_substream;
 
 	for (i = 0; i < urb->number_of_packets; i++) {
 		unsigned int frames_for_packet;
@@ -224,15 +202,28 @@ void playback_urb_complete(struct urb *urb)
 	}
 	urb->transfer_buffer_length = total_bytes_for_urb;
 
-	if (total_bytes_for_urb > 0) {
+	if (total_bytes_for_urb == 0) {
-		if (substream) {
+		spin_unlock_irqrestore(&tascam->lock, flags);
+		goto resubmit;
+	}
+
+	if (!substream) {
+		memset(urb->transfer_buffer, 0, total_bytes_for_urb);
+		spin_unlock_irqrestore(&tascam->lock, flags);
+		goto resubmit;
+	}
+
 	runtime = substream->runtime;
+	size_t playback_pos = tascam->driver_playback_pos;
+	spin_unlock_irqrestore(&tascam->lock, flags);
+
+	/* Copy from ALSA DMA buffer - outside of the main device lock */
 	u8 *dst_buf = urb->transfer_buffer;
-			size_t ptr_bytes = frames_to_bytes(runtime, tascam->driver_playback_pos);
+	size_t ptr_bytes = frames_to_bytes(runtime, playback_pos);
 	frames_to_copy = bytes_to_frames(runtime, total_bytes_for_urb);
 
-			if (tascam->driver_playback_pos + frames_to_copy > runtime->buffer_size) {
+	if (playback_pos + frames_to_copy > runtime->buffer_size) {
-				size_t part1 = runtime->buffer_size - tascam->driver_playback_pos;
+		size_t part1 = runtime->buffer_size - playback_pos;
 		size_t part1_bytes = frames_to_bytes(runtime, part1);
 
 		memcpy(dst_buf, runtime->dma_area + ptr_bytes, part1_bytes);
@@ -241,33 +232,38 @@ void playback_urb_complete(struct urb *urb)
 		memcpy(dst_buf, runtime->dma_area + ptr_bytes, total_bytes_for_urb);
 	}
 
+	/* Re-acquire lock to update shared stream state */
+	spin_lock_irqsave(&tascam->lock, flags);
 	tascam->driver_playback_pos += frames_to_copy;
 	if (tascam->driver_playback_pos >= runtime->buffer_size)
 		tascam->driver_playback_pos -= runtime->buffer_size;
 
 	tascam->playback_frames_consumed += frames_to_copy;
 
-			if (div_u64(tascam->playback_frames_consumed, runtime->period_size) > tascam->last_pb_period_pos) {
+	if (runtime->period_size > 0 && 
+		div_u64(tascam->playback_frames_consumed, runtime->period_size) > tascam->last_pb_period_pos) {
 		tascam->last_pb_period_pos = div_u64(tascam->playback_frames_consumed, runtime->period_size);
 		need_period_elapsed = true;
 	}
-		} else {
-			memset(urb->transfer_buffer, 0, total_bytes_for_urb);
-		}
-	}
 	spin_unlock_irqrestore(&tascam->lock, flags);
 
+resubmit:
+
+	usb_anchor_urb(urb, &tascam->playback_anchor);
+	if (usb_submit_urb(urb, GFP_ATOMIC) < 0) {
+		goto exit_clear_locked;
+	}
+
 	if (need_period_elapsed && substream)
 		snd_pcm_period_elapsed(substream);
 
-	usb_anchor_urb(urb, &tascam->playback_anchor);
-	if (usb_submit_urb(urb, GFP_ATOMIC) < 0)
-		goto exit_clear;
-
 	return;
 
+exit_clear_locked:
+	spin_lock_irqsave(&tascam->lock, flags);
 exit_clear:
 	usb_unanchor_urb(urb);
+	spin_unlock_irqrestore(&tascam->lock, flags);
 	atomic_dec(&tascam->active_urbs);
 }
 
@@ -288,7 +284,8 @@ void feedback_urb_complete(struct urb *urb)
 	unsigned long flags;
 	int p;
 
-	if (urb->status || !tascam || !atomic_read(&tascam->playback_active)) {
+	if (urb->status || !tascam || 
+		(!atomic_read(&tascam->playback_active) && !tascam->running_ghost_playback)) {
 		usb_unanchor_urb(urb);
 		atomic_dec(&tascam->active_urbs);
 		return;