[PATCH 1/5] usb: gadget: f_midi: refactor state machine

Felipe F. Tonello
2016-03-02T19:40:49Z

This refactor results in a cleaner state machine code and as a result fixed a
bug when packaging a USB-MIDI packet right after a non-conformant MIDI byte stream.

Signed-off-by: Felipe F. Tonello <eu@felipetonello.com>
---
drivers/usb/gadget/function/f_midi.c | 204 ++++++++++++++++++++++-------------
1 file changed, 129 insertions(+), 75 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index 84c0ee5ebd1e..3cdb0741f3f8 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -50,6 +50,19 @@ static const char f_midi_longname[] = "MIDI Gadget";
*/
#define MAX_PORTS 16

+/* MIDI message states */
+enum {
+ STATE_INITIAL = 0, /* pseudo state */
+ STATE_1PARAM,
+ STATE_2PARAM_1,
+ STATE_2PARAM_2,
+ STATE_SYSEX_0,
+ STATE_SYSEX_1,
+ STATE_SYSEX_2,
+ STATE_REAL_TIME,
+ STATE_FINISHED, /* pseudo state */
+};
+
/*
* This is a gadget, and the IN/OUT naming is from the host's perspective.
* USB -> OUT endpoint -> rawmidi
@@ -60,13 +73,6 @@ struct gmidi_in_port {
int active;
uint8_t cable;
uint8_t state;
-#define STATE_UNKNOWN 0
-#define STATE_1PARAM 1
-#define STATE_2PARAM_1 2
-#define STATE_2PARAM_2 3
-#define STATE_SYSEX_0 4
-#define STATE_SYSEX_1 5
-#define STATE_SYSEX_2 6
uint8_t data[2];
};

@@ -400,118 +406,166 @@ static int f_midi_snd_free(struct snd_device *device)
return 0;
}

-static void f_midi_transmit_packet(struct usb_request *req, uint8_t p0,
- uint8_t p1, uint8_t p2, uint8_t p3)
-{
- unsigned length = req->length;
- u8 *buf = (u8 *)req->buf + length;
-
- buf[0] = p0;
- buf[1] = p1;
- buf[2] = p2;
- buf[3] = p3;
- req->length = length + 4;
-}
-
/*
* Converts MIDI commands to USB MIDI packets.
*/
static void f_midi_transmit_byte(struct usb_request *req,
struct gmidi_in_port *port, uint8_t b)
{
- uint8_t p0 = port->cable << 4;
+ uint8_t p[4] = { port->cable << 4, 0, 0, 0 };
+ uint8_t next_state = STATE_INITIAL;
+
+ switch (b) {
+ case 0xf8 ... 0xff:
+ /* System Real-Time Messages */
+ p[0] |= 0x0f;
+ p[1] = b;
+ next_state = port->state;
+ port->state = STATE_REAL_TIME;
+ break;
+
+ case 0xf7:
+ /* End of SysEx */
+ switch (port->state) {
+ case STATE_SYSEX_0:
+ p[0] |= 0x05;
+ p[1] = 0xf7;
+ next_state = STATE_FINISHED;
+ break;
+ case STATE_SYSEX_1:
+ p[0] |= 0x06;
+ p[1] = port->data[0];
+ p[2] = 0xf7;
+ next_state = STATE_FINISHED;
+ break;
+ case STATE_SYSEX_2:
+ p[0] |= 0x07;
+ p[1] = port->data[0];
+ p[2] = port->data[1];
+ p[3] = 0xf7;
+ next_state = STATE_FINISHED;
+ break;
+ default:
+ /* Ignore byte */
+ next_state = port->state;
+ port->state = STATE_INITIAL;
+ }
+ break;

- if (b >= 0xf8) {
- f_midi_transmit_packet(req, p0 | 0x0f, b, 0, 0);
- } else if (b >= 0xf0) {
+ case 0xf0 ... 0xf6:
+ /* System Common Messages */
+ port->data[0] = port->data[1] = 0;
+ port->state = STATE_INITIAL;
switch (b) {
case 0xf0:
port->data[0] = b;
- port->state = STATE_SYSEX_1;
+ port->data[1] = 0;
+ next_state = STATE_SYSEX_1;
break;
case 0xf1:
case 0xf3:
port->data[0] = b;
- port->state = STATE_1PARAM;
+ next_state = STATE_1PARAM;
break;
case 0xf2:
port->data[0] = b;
- port->state = STATE_2PARAM_1;
+ next_state = STATE_2PARAM_1;
break;
case 0xf4:
case 0xf5:
- port->state = STATE_UNKNOWN;
+ next_state = STATE_INITIAL;
break;
case 0xf6:
- f_midi_transmit_packet(req, p0 | 0x05, 0xf6, 0, 0);
- port->state = STATE_UNKNOWN;
- break;
- case 0xf7:
- switch (port->state) {
- case STATE_SYSEX_0:
- f_midi_transmit_packet(req,
- p0 | 0x05, 0xf7, 0, 0);
- break;
- case STATE_SYSEX_1:
- f_midi_transmit_packet(req,
- p0 | 0x06, port->data[0], 0xf7, 0);
- break;
- case STATE_SYSEX_2:
- f_midi_transmit_packet(req,
- p0 | 0x07, port->data[0],
- port->data[1], 0xf7);
- break;
- }
- port->state = STATE_UNKNOWN;
+ p[0] |= 0x05;
+ p[1] = 0xf6;
+ next_state = STATE_FINISHED;
break;
}
- } else if (b >= 0x80) {
+ break;
+
+ case 0x80 ... 0xef:
+ /*
+ * Channel Voice Messages, Channel Mode Messages
+ * and Control Change Messages.
+ */
port->data[0] = b;
+ port->data[1] = 0;
+ port->state = STATE_INITIAL;
if (b >= 0xc0 && b <= 0xdf)
- port->state = STATE_1PARAM;
+ next_state = STATE_1PARAM;
else
- port->state = STATE_2PARAM_1;
- } else { /* b < 0x80 */
+ next_state = STATE_2PARAM_1;
+ break;
+
+ case 0x00 ... 0x7f:
+ /* Message parameters */
switch (port->state) {
case STATE_1PARAM:
- if (port->data[0] < 0xf0) {
- p0 |= port->data[0] >> 4;
- } else {
- p0 |= 0x02;
- port->state = STATE_UNKNOWN;
- }
- f_midi_transmit_packet(req, p0, port->data[0], b, 0);
+ if (port->data[0] < 0xf0)
+ p[0] |= port->data[0] >> 4;
+ else
+ p[0] |= 0x02;
+
+ p[1] = port->data[0];
+ p[2] = b;
+ /* This is to allow Running State Messages */
+ next_state = STATE_1PARAM;
break;
case STATE_2PARAM_1:
port->data[1] = b;
- port->state = STATE_2PARAM_2;
+ next_state = STATE_2PARAM_2;
break;
case STATE_2PARAM_2:
- if (port->data[0] < 0xf0) {
- p0 |= port->data[0] >> 4;
- port->state = STATE_2PARAM_1;
- } else {
- p0 |= 0x03;
- port->state = STATE_UNKNOWN;
- }
- f_midi_transmit_packet(req,
- p0, port->data[0], port->data[1], b);
+ if (port->data[0] < 0xf0)
+ p[0] |= port->data[0] >> 4;
+ else
+ p[0] |= 0x03;
+
+ p[1] = port->data[0];
+ p[2] = port->data[1];
+ p[3] = b;
+ /* This is to allow Running State Messages */
+ next_state = STATE_2PARAM_1;
break;
case STATE_SYSEX_0:
port->data[0] = b;
- port->state = STATE_SYSEX_1;
+ next_state = STATE_SYSEX_1;
break;
case STATE_SYSEX_1:
port->data[1] = b;
- port->state = STATE_SYSEX_2;
+ next_state = STATE_SYSEX_2;
break;
case STATE_SYSEX_2:
- f_midi_transmit_packet(req,
- p0 | 0x04, port->data[0], port->data[1], b);
- port->state = STATE_SYSEX_0;
+ p[0] |= 0x04;
+ p[1] = port->data[0];
+ p[2] = port->data[1];
+ p[3] = b;
+ next_state = STATE_SYSEX_0;
break;
}
+ break;
+ }
+
+ /* States where we have to write into the USB request */
+ if (next_state == STATE_FINISHED ||
+ port->state == STATE_SYSEX_2 ||
+ port->state == STATE_1PARAM ||
+ port->state == STATE_2PARAM_2 ||
+ port->state == STATE_REAL_TIME) {
+
+ unsigned length = req->length;
+ u8 *buf = (u8 *)req->buf + length;
+
+ memcpy(buf, p, sizeof(p));
+ req->length = length + sizeof(p);
+
+ if (next_state == STATE_FINISHED) {
+ next_state = STATE_INITIAL;
+ port->data[0] = port->data[1] = 0;
+ }
}
+
+ port->state = next_state;
}

static void f_midi_drop_out_substreams(struct f_midi *midi)
@@ -631,7 +685,7 @@ static int f_midi_in_open(struct snd_rawmidi_substream *substream)
VDBG(midi, "%s()\n", __func__);
port = midi->in_ports_array + substream->number;
port->substream = substream;
- port->state = STATE_UNKNOWN;
+ port->state = STATE_INITIAL;
return 0;
}

--
2.7.2