[PATCH 1/1] sound: rawmidi: Add framing mode

[David Henningsson]

This commit adds a new framing mode that frames all MIDI data into
16-byte frames with a timestamp from the monotonic_raw clock.

The main benefit is that we can get accurate timestamps even if
userspace wakeup and processing is not immediate.
---
 include/sound/rawmidi.h     |  1 +
 include/uapi/sound/asound.h | 18 ++++++++++++++-
 sound/core/rawmidi.c        | 45 ++++++++++++++++++++++++++++++++++++-
 3 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h
index 334842daa904..ea4d88d513e1 100644
--- a/include/sound/rawmidi.h
+++ b/include/sound/rawmidi.h
@@ -81,6 +81,7 @@ struct snd_rawmidi_substream {
 	bool opened;			/* open flag */
 	bool append;			/* append flag (merge more streams) */
 	bool active_sensing;		/* send active sensing when close */
+	u8 framing; /* whether to frame data (for input) */
 	int use_count;			/* use counter (for output) */
 	size_t bytes;
 	struct snd_rawmidi *rmidi;
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 535a7229e1d9..13c3865a818e 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -736,12 +736,28 @@ struct snd_rawmidi_info {
 	unsigned char reserved[64];	/* reserved for future use */
 };
 
+enum {
+	SNDRV_RAWMIDI_FRAMING_NONE = 0,
+	SNDRV_RAWMIDI_FRAMING_TSTAMP_MONOTONIC_RAW,
+	SNDRV_RAWMIDI_FRAMING_LAST = SNDRV_RAWMIDI_FRAMING_TSTAMP_MONOTONIC_RAW,
+};
+
+#define SND_RAWMIDI_FRAMING_DATA_LENGTH 7
+
+struct snd_rawmidi_framing_tstamp {
+	unsigned int tv_sec;	/* seconds */
+	unsigned int tv_nsec;	/* nanoseconds */
+	unsigned char length;
+	unsigned char data[SND_RAWMIDI_FRAMING_DATA_LENGTH];
+};
+
 struct snd_rawmidi_params {
 	int stream;
 	size_t buffer_size;		/* queue size in bytes */
 	size_t avail_min;		/* minimum avail bytes for wakeup */
 	unsigned int no_active_sensing: 1; /* do not send active sensing byte in close() */
-	unsigned char reserved[16];	/* reserved for future use */
+	unsigned char framing; /* For input data only, frame incoming data */
+	unsigned char reserved[15];	/* reserved for future use */
 };
 
 #ifndef __KERNEL__
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index aca00af93afe..fefa7d9b70a6 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -721,6 +721,7 @@ int snd_rawmidi_input_params(struct snd_rawmidi_substream *substream,
 			     struct snd_rawmidi_params *params)
 {
 	snd_rawmidi_drain_input(substream);
+	substream->framing = params->framing;
 	return resize_runtime_buffer(substream->runtime, params, true);
 }
 EXPORT_SYMBOL(snd_rawmidi_input_params);
@@ -963,6 +964,44 @@ static int snd_rawmidi_control_ioctl(struct snd_card *card,
 	return -ENOIOCTLCMD;
 }
 
+static int receive_with_tstamp_framing(struct snd_rawmidi_substream *substream,
+			const unsigned char *buffer, int src_count, struct timespec64 *tstamp)
+{
+	struct snd_rawmidi_runtime *runtime = substream->runtime;
+	struct snd_rawmidi_framing_tstamp frame;
+	struct snd_rawmidi_framing_tstamp *dest_ptr;
+
+	int dest_frames = 0;
+	int frame_size = sizeof(struct snd_rawmidi_framing_tstamp);
+	frame.tv_sec = tstamp->tv_sec;
+	frame.tv_nsec = tstamp->tv_nsec;
+
+	if (snd_BUG_ON(runtime->hw_ptr & 15 || runtime->buffer_size & 15 || frame_size != 16))
+		return -EINVAL;
+	while (src_count > 0) {
+		if ((int)(runtime->buffer_size - runtime->avail) < frame_size) {
+			runtime->xruns += src_count;
+			return dest_frames * frame_size;
+		}
+		if (SND_RAWMIDI_FRAMING_DATA_LENGTH < src_count)
+			frame.length = SND_RAWMIDI_FRAMING_DATA_LENGTH;
+		else {
+			frame.length = src_count;
+			memset(frame.data, 0, SND_RAWMIDI_FRAMING_DATA_LENGTH);
+		}
+		memcpy(frame.data, buffer, frame.length);
+		buffer += frame.length;
+		src_count -= frame.length;
+		dest_ptr = (struct snd_rawmidi_framing_tstamp *) (runtime->buffer + runtime->hw_ptr);
+		*dest_ptr = frame;
+		runtime->avail += frame_size;
+		runtime->hw_ptr += frame_size;
+		runtime->hw_ptr %= runtime->buffer_size;
+		dest_frames++;
+	}
+	return dest_frames * frame_size;
+}
+
 /**
  * snd_rawmidi_receive - receive the input data from the device
  * @substream: the rawmidi substream
@@ -988,7 +1027,11 @@ int snd_rawmidi_receive(struct snd_rawmidi_substream *substream,
 		return -EINVAL;
 	}
 	spin_lock_irqsave(&runtime->lock, flags);
-	if (count == 1) {	/* special case, faster code */
+	if (substream->framing == SNDRV_RAWMIDI_FRAMING_TSTAMP_MONOTONIC_RAW) {
+		struct timespec64 ts64;
+		ktime_get_raw_ts64(&ts64);
+		result = receive_with_tstamp_framing(substream, buffer, count, &ts64);
+	} else if (count == 1) {	/* special case, faster code */
 		substream->bytes++;
 		if (runtime->avail < runtime->buffer_size) {
 			runtime->buffer[runtime->hw_ptr++] = buffer[0];
-- 
2.25.1