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 */