5 files changed, 65 insertions, 24 deletions

diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
index 3badc70124ab..0d580186ef1a 100644
--- a/sound/firewire/amdtp.c
+++ b/sound/firewire/amdtp.c
@@ -21,7 +21,19 @@
 #define CYCLES_PER_SECOND	8000
 #define TICKS_PER_SECOND	(TICKS_PER_CYCLE * CYCLES_PER_SECOND)
 
-#define TRANSFER_DELAY_TICKS	0x2e00 /* 479.17 µs */
+/*
+ * Nominally 3125 bytes/second, but the MIDI port's clock might be
+ * 1% too slow, and the bus clock 100 ppm too fast.
+ */
+#define MIDI_BYTES_PER_SECOND	3093
+
+/*
+ * Several devices look only at the first eight data blocks.
+ * In any case, this is more than enough for the MIDI data rate.
+ */
+#define MAX_MIDI_RX_BLOCKS	8
+
+#define TRANSFER_DELAY_TICKS	0x2e00 /* 479.17 µs */
 
 /* isochronous header parameters */
 #define ISO_DATA_LENGTH_SHIFT	16
@@ -78,8 +90,6 @@ int amdtp_stream_init(struct amdtp_stream *s, struct fw_unit *unit,
 	s->callbacked = false;
 	s->sync_slave = NULL;
 
-	s->rx_blocks_for_midi = UINT_MAX;
-
 	return 0;
 }
 EXPORT_SYMBOL(amdtp_stream_init);
@@ -222,6 +232,14 @@ sfc_found:
 	for (i = 0; i < pcm_channels; i++)
 		s->pcm_positions[i] = i;
 	s->midi_position = s->pcm_channels;
+
+	/*
+	 * We do not know the actual MIDI FIFO size of most devices.  Just
+	 * assume two bytes, i.e., one byte can be received over the bus while
+	 * the previous one is transmitted over MIDI.
+	 * (The value here is adjusted for midi_ratelimit_per_packet().)
+	 */
+	s->midi_fifo_limit = rate - MIDI_BYTES_PER_SECOND * s->syt_interval + 1;
 }
 EXPORT_SYMBOL(amdtp_stream_set_parameters);
 
@@ -463,6 +481,36 @@ static void amdtp_fill_pcm_silence(struct amdtp_stream *s,
 	}
 }
 
+/*
+ * To avoid sending MIDI bytes at too high a rate, assume that the receiving
+ * device has a FIFO, and track how much it is filled.  This values increases
+ * by one whenever we send one byte in a packet, but the FIFO empties at
+ * a constant rate independent of our packet rate.  One packet has syt_interval
+ * samples, so the number of bytes that empty out of the FIFO, per packet(!),
+ * is MIDI_BYTES_PER_SECOND * syt_interval / sample_rate.  To avoid storing
+ * fractional values, the values in midi_fifo_used[] are measured in bytes
+ * multiplied by the sample rate.
+ */
+static bool midi_ratelimit_per_packet(struct amdtp_stream *s, unsigned int port)
+{
+	int used;
+
+	used = s->midi_fifo_used[port];
+	if (used == 0) /* common shortcut */
+		return true;
+
+	used -= MIDI_BYTES_PER_SECOND * s->syt_interval;
+	used = max(used, 0);
+	s->midi_fifo_used[port] = used;
+
+	return used < s->midi_fifo_limit;
+}
+
+static void midi_rate_use_one_byte(struct amdtp_stream *s, unsigned int port)
+{
+	s->midi_fifo_used[port] += amdtp_rate_table[s->sfc];
+}
+
 static void amdtp_fill_midi(struct amdtp_stream *s,
 			    __be32 *buffer, unsigned int frames)
 {
@@ -470,16 +518,21 @@ static void amdtp_fill_midi(struct amdtp_stream *s,
 	u8 *b;
 
 	for (f = 0; f < frames; f++) {
-		buffer[s->midi_position] = 0;
 		b = (u8 *)&buffer[s->midi_position];
 
 		port = (s->data_block_counter + f) % 8;
-		if ((f >= s->rx_blocks_for_midi) ||
-		    (s->midi[port] == NULL) ||
-		    (snd_rawmidi_transmit(s->midi[port], b + 1, 1) <= 0))
-			b[0] = 0x80;
-		else
+		if (f < MAX_MIDI_RX_BLOCKS &&
+		    midi_ratelimit_per_packet(s, port) &&
+		    s->midi[port] != NULL &&
+		    snd_rawmidi_transmit(s->midi[port], &b[1], 1) == 1) {
+			midi_rate_use_one_byte(s, port);
 			b[0] = 0x81;
+		} else {
+			b[0] = 0x80;
+			b[1] = 0;
+		}
+		b[2] = 0;
+		b[3] = 0;
 
 		buffer += s->data_block_quadlets;
 	}
diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h
index e6e8926275b0..8a03a91e728b 100644
--- a/sound/firewire/amdtp.h
+++ b/sound/firewire/amdtp.h
@@ -148,13 +148,12 @@ struct amdtp_stream {
 	bool double_pcm_frames;
 
 	struct snd_rawmidi_substream *midi[AMDTP_MAX_CHANNELS_FOR_MIDI * 8];
+	int midi_fifo_limit;
+	int midi_fifo_used[AMDTP_MAX_CHANNELS_FOR_MIDI * 8];
 
 	/* quirk: fixed interval of dbc between previos/current packets. */
 	unsigned int tx_dbc_interval;
 
-	/* quirk: the first count of data blocks in an rx packet for MIDI */
-	unsigned int rx_blocks_for_midi;
-
 	bool callbacked;
 	wait_queue_head_t callback_wait;
 	struct amdtp_stream *sync_slave;
diff --git a/sound/firewire/bebob/bebob_stream.c b/sound/firewire/bebob/bebob_stream.c
index 1aab0a32870c..0ebcabfdc7ce 100644
--- a/sound/firewire/bebob/bebob_stream.c
+++ b/sound/firewire/bebob/bebob_stream.c
@@ -484,13 +484,6 @@ int snd_bebob_stream_init_duplex(struct snd_bebob *bebob)
 		amdtp_stream_destroy(&bebob->rx_stream);
 		destroy_both_connections(bebob);
 	}
-	/*
-	 * The firmware for these devices ignore MIDI messages in more than
-	 * first 8 data blocks of an received AMDTP packet.
-	 */
-	if (bebob->spec == &maudio_fw410_spec ||
-	    bebob->spec == &maudio_special_spec)
-		bebob->rx_stream.rx_blocks_for_midi = 8;
 end:
 	return err;
 }
diff --git a/sound/firewire/fireworks/fireworks_stream.c b/sound/firewire/fireworks/fireworks_stream.c
index b985fc5ebdc6..4f440e163667 100644
--- a/sound/firewire/fireworks/fireworks_stream.c
+++ b/sound/firewire/fireworks/fireworks_stream.c
@@ -179,11 +179,6 @@ int snd_efw_stream_init_duplex(struct snd_efw *efw)
 		destroy_stream(efw, &efw->tx_stream);
 		goto end;
 	}
-	/*
-	 * Fireworks ignores MIDI messages in more than first 8 data
-	 * blocks of an received AMDTP packet.
-	 */
-	efw->rx_stream.rx_blocks_for_midi = 8;
 
 	/* set IEC61883 compliant mode (actually not fully compliant...) */
 	err = snd_efw_command_set_tx_mode(efw, SND_EFW_TRANSPORT_MODE_IEC61883);
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 41650d5b93b7..3e2ef61c627b 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -913,6 +913,7 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
 	case USB_ID(0x046d, 0x0807): /* Logitech Webcam C500 */
 	case USB_ID(0x046d, 0x0808):
 	case USB_ID(0x046d, 0x0809):
+	case USB_ID(0x046d, 0x0819): /* Logitech Webcam C210 */
 	case USB_ID(0x046d, 0x081b): /* HD Webcam c310 */
 	case USB_ID(0x046d, 0x081d): /* HD Webcam c510 */
 	case USB_ID(0x046d, 0x0825): /* HD Webcam c270 */