Re: [PATCH] USB: ftdi_sio: Remove tty->low_latency.

From: Johan Hovold
Date: Sat Oct 03 2009 - 10:41:24 EST

On Sat, Oct 03, 2009 at 02:28:48PM +0200, Johan Hovold wrote:
> Duh. :) Here's an update that uses both throttle flags which is of
> course required.

A minor update which processes every packet including status only ones.

/Johan

From: Johan Hovold <jhovold@xxxxxxxxx>
Date: Sat, 3 Oct 2009 12:30:13 +0200
Subject: [PATCH] USB: ftdi_sio: Rewrite.

- Remove work queue.
- Use urb status to determine when port is closed rather than port
count. (Fixes stalled reads due to open race on 2.6.31).
- Re-structure read processing.
- Use tty_insert_flip_string instead of per character push unless
console.
- Always process before throttling.
- Handle late call to unthrottle during serial_close by checking
ASYNCB_CLOSING.
- Remove rx_flags and lock and use flags in usb_serial_port instead.
- Remove unused rx_bytes counter.
---
drivers/usb/serial/ftdi_sio.c | 431 ++++++++++++++---------------------------
1 files changed, 146 insertions(+), 285 deletions(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 0ac2c2f..287f2df 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -76,12 +76,7 @@ struct ftdi_private {
unsigned long last_dtr_rts; /* saved modem control outputs */
wait_queue_head_t delta_msr_wait; /* Used for TIOCMIWAIT */
char prev_status, diff_status; /* Used for TIOCMIWAIT */
- __u8 rx_flags; /* receive state flags (throttling) */
- spinlock_t rx_lock; /* spinlock for receive state */
- struct delayed_work rx_work;
struct usb_serial_port *port;
- int rx_processed;
- unsigned long rx_bytes;

__u16 interface; /* FT2232C, FT2232H or FT4232H port interface
(0 for FT232/245) */
@@ -737,10 +732,6 @@ static const char *ftdi_chip_name[] = {
/* Constants for read urb and write urb */
#define BUFSZ 512

-/* rx_flags */
-#define THROTTLED 0x01
-#define ACTUALLY_THROTTLED 0x02
-
/* Used for TIOCMIWAIT */
#define FTDI_STATUS_B0_MASK (FTDI_RS0_CTS | FTDI_RS0_DSR | FTDI_RS0_RI | FTDI_RS0_RLSD)
#define FTDI_STATUS_B1_MASK (FTDI_RS_BI)
@@ -763,7 +754,7 @@ static int ftdi_write_room(struct tty_struct *tty);
static int ftdi_chars_in_buffer(struct tty_struct *tty);
static void ftdi_write_bulk_callback(struct urb *urb);
static void ftdi_read_bulk_callback(struct urb *urb);
-static void ftdi_process_read(struct work_struct *work);
+static void ftdi_process_read(struct usb_serial_port *port);
static void ftdi_set_termios(struct tty_struct *tty,
struct usb_serial_port *port, struct ktermios *old);
static int ftdi_tiocmget(struct tty_struct *tty, struct file *file);
@@ -1526,7 +1517,6 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
}

kref_init(&priv->kref);
- spin_lock_init(&priv->rx_lock);
spin_lock_init(&priv->tx_lock);
init_waitqueue_head(&priv->delta_msr_wait);
/* This will push the characters through immediately rather
@@ -1548,7 +1538,6 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
port->read_urb->transfer_buffer_length = BUFSZ;
}

- INIT_DELAYED_WORK(&priv->rx_work, ftdi_process_read);
priv->port = port;

/* Free port's existing write urb and transfer buffer. */
@@ -1685,6 +1674,26 @@ static int ftdi_sio_port_remove(struct usb_serial_port *port)
return 0;
}

+int ftdi_submit_read_urb(struct usb_serial_port *port, gfp_t mem_flags)
+{
+ struct urb *urb = port->read_urb;
+ struct usb_serial *serial = port->serial;
+ int result;
+
+ usb_fill_bulk_urb(urb, serial->dev,
+ usb_rcvbulkpipe(serial->dev,
+ port->bulk_in_endpointAddress),
+ urb->transfer_buffer,
+ urb->transfer_buffer_length,
+ ftdi_read_bulk_callback, port);
+ result = usb_submit_urb(urb, mem_flags);
+ if (result)
+ dev_err(&port->dev,
+ "%s - failed submitting read urb, error %d\n",
+ __func__, result);
+ return result;
+}
+
static int ftdi_open(struct tty_struct *tty, struct usb_serial_port *port)
{ /* ftdi_open */
struct usb_device *dev = port->serial->dev;
@@ -1699,9 +1708,6 @@ static int ftdi_open(struct tty_struct *tty, struct usb_serial_port *port)
spin_lock_irqsave(&priv->tx_lock, flags);
priv->tx_bytes = 0;
spin_unlock_irqrestore(&priv->tx_lock, flags);
- spin_lock_irqsave(&priv->rx_lock, flags);
- priv->rx_bytes = 0;
- spin_unlock_irqrestore(&priv->rx_lock, flags);

write_latency_timer(port);

@@ -1721,23 +1727,14 @@ static int ftdi_open(struct tty_struct *tty, struct usb_serial_port *port)
ftdi_set_termios(tty, port, tty->termios);

/* Not throttled */
- spin_lock_irqsave(&priv->rx_lock, flags);
- priv->rx_flags &= ~(THROTTLED | ACTUALLY_THROTTLED);
- spin_unlock_irqrestore(&priv->rx_lock, flags);
+ spin_lock_irqsave(&port->lock, flags);
+ port->throttled = 0;
+ port->throttle_req = 0;
+ spin_unlock_irqrestore(&port->lock, flags);

/* Start reading from the device */
- priv->rx_processed = 0;
- usb_fill_bulk_urb(port->read_urb, dev,
- usb_rcvbulkpipe(dev, port->bulk_in_endpointAddress),
- port->read_urb->transfer_buffer,
- port->read_urb->transfer_buffer_length,
- ftdi_read_bulk_callback, port);
- result = usb_submit_urb(port->read_urb, GFP_KERNEL);
- if (result)
- dev_err(&port->dev,
- "%s - failed submitting read urb, error %d\n",
- __func__, result);
- else
+ result = ftdi_submit_read_urb(port, GFP_KERNEL);
+ if (!result)
kref_get(&priv->kref);

return result;
@@ -1783,10 +1780,6 @@ static void ftdi_close(struct usb_serial_port *port)

dbg("%s", __func__);

-
- /* cancel any scheduled reading */
- cancel_delayed_work_sync(&priv->rx_work);
-
/* shutdown our bulk read */
usb_kill_urb(port->read_urb);
kref_put(&priv->kref, ftdi_sio_priv_release);
@@ -2009,271 +2002,142 @@ static int ftdi_chars_in_buffer(struct tty_struct *tty)
return buffered;
}

-static void ftdi_read_bulk_callback(struct urb *urb)
+static int ftdi_process_packet(struct tty_struct *tty,
+ struct usb_serial_port *port, struct ftdi_private *priv,
+ char *packet, int len)
{
- struct usb_serial_port *port = urb->context;
- struct tty_struct *tty;
- struct ftdi_private *priv;
- unsigned long countread;
- unsigned long flags;
- int status = urb->status;
-
- if (urb->number_of_packets > 0) {
- dev_err(&port->dev, "%s transfer_buffer_length %d "
- "actual_length %d number of packets %d\n", __func__,
- urb->transfer_buffer_length,
- urb->actual_length, urb->number_of_packets);
- dev_err(&port->dev, "%s transfer_flags %x\n", __func__,
- urb->transfer_flags);
- }
+ int i;
+ char status;
+ char flag;
+ char *ch;

dbg("%s - port %d", __func__, port->number);

- if (port->port.count <= 0)
- return;
-
- tty = tty_port_tty_get(&port->port);
- if (!tty) {
- dbg("%s - bad tty pointer - exiting", __func__);
- return;
+ if (len < 2) {
+ dbg("malformed packet");
+ return 0;
}

- priv = usb_get_serial_port_data(port);
- if (!priv) {
- dbg("%s - bad port private data pointer - exiting", __func__);
- goto out;
+ /* Compare new line status to the old one, signal if different/
+ N.B. packet may be processed more than once, but differences
+ are only processed once. */
+ status = packet[0] & FTDI_STATUS_B0_MASK;
+ if (status != priv->prev_status) {
+ priv->diff_status |= status ^ priv->prev_status;
+ wake_up_interruptible(&priv->delta_msr_wait);
+ priv->prev_status = status;
}

- if (urb != port->read_urb)
- dev_err(&port->dev, "%s - Not my urb!\n", __func__);
-
- if (status) {
- /* This will happen at close every time so it is a dbg not an
- err */
- dbg("(this is ok on close) nonzero read bulk status received: %d", status);
- goto out;
+ /*
+ * Although the device uses a bitmask and hence can have multiple
+ * errors on a packet - the order here sets the priority the error is
+ * returned to the tty layer.
+ */
+ flag = TTY_NORMAL;
+ if (packet[1] & FTDI_RS_OE) {
+ flag = TTY_OVERRUN;
+ dbg("OVERRRUN error");
}
-
- /* count data bytes, but not status bytes */
- countread = urb->actual_length;
- countread -= 2 * DIV_ROUND_UP(countread, priv->max_packet_size);
- spin_lock_irqsave(&priv->rx_lock, flags);
- priv->rx_bytes += countread;
- spin_unlock_irqrestore(&priv->rx_lock, flags);
-
- ftdi_process_read(&priv->rx_work.work);
-out:
- tty_kref_put(tty);
-} /* ftdi_read_bulk_callback */
-
-
-static void ftdi_process_read(struct work_struct *work)
-{ /* ftdi_process_read */
- struct ftdi_private *priv =
- container_of(work, struct ftdi_private, rx_work.work);
- struct usb_serial_port *port = priv->port;
- struct urb *urb;
- struct tty_struct *tty;
- char error_flag;
- unsigned char *data;
-
- int i;
- int result;
- int need_flip;
- int packet_offset;
- unsigned long flags;
-
- dbg("%s - port %d", __func__, port->number);
-
- if (port->port.count <= 0)
- return;
-
- tty = tty_port_tty_get(&port->port);
- if (!tty) {
- dbg("%s - bad tty pointer - exiting", __func__);
- return;
+ if (packet[1] & FTDI_RS_BI) {
+ flag = TTY_BREAK;
+ dbg("BREAK received");
+ usb_serial_handle_break(port);
}
-
- priv = usb_get_serial_port_data(port);
- if (!priv) {
- dbg("%s - bad port private data pointer - exiting", __func__);
- goto out;
+ if (packet[1] & FTDI_RS_PE) {
+ flag = TTY_PARITY;
+ dbg("PARITY error");
}
-
- urb = port->read_urb;
- if (!urb) {
- dbg("%s - bad read_urb pointer - exiting", __func__);
- goto out;
+ if (packet[1] & FTDI_RS_FE) {
+ flag = TTY_FRAME;
+ dbg("FRAMING error");
}

- data = urb->transfer_buffer;
-
- if (priv->rx_processed) {
- dbg("%s - already processed: %d bytes, %d remain", __func__,
- priv->rx_processed,
- urb->actual_length - priv->rx_processed);
- } else {
- /* The first two bytes of every read packet are status */
- if (urb->actual_length > 2)
- usb_serial_debug_data(debug, &port->dev, __func__,
- urb->actual_length, data);
- else
- dbg("Status only: %03oo %03oo", data[0], data[1]);
+ len -= 2;
+ if (!len)
+ return 0; /* status only */
+ ch = packet + 2;
+ /*
+ * The per character mucking around with sysrq path it too slow, so
+ * shortcircuit it in the 99.9999999% of cases where the USB serial is
+ * not a console anyway.
+ */
+ if (!port->console || !port->sysrq)
+ tty_insert_flip_string(tty, ch, len);
+ else {
+ for (i = 0; i < len; i++, ch++) {
+ if (!usb_serial_handle_sysrq_char(tty, port, *ch))
+ tty_insert_flip_char(tty, *ch, flag);
+ }
}
+ return len;
+}

+static void ftdi_process_read(struct usb_serial_port *port)
+{
+ struct urb *urb = port->read_urb;
+ struct tty_struct *tty;
+ struct ftdi_private *priv = usb_get_serial_port_data(port);
+ char *data = (char *)urb->transfer_buffer;
+ int i;
+ int len;
+ int count = 0;

- /* TO DO -- check for hung up line and handle appropriately: */
- /* send hangup */
- /* See acm.c - you do a tty_hangup - eg tty_hangup(tty) */
- /* if CD is dropped and the line is not CLOCAL then we should hangup */
-
- need_flip = 0;
- for (packet_offset = priv->rx_processed;
- packet_offset < urb->actual_length; packet_offset += priv->max_packet_size) {
- int length;
-
- /* Compare new line status to the old one, signal if different/
- N.B. packet may be processed more than once, but differences
- are only processed once. */
- char new_status = data[packet_offset + 0] &
- FTDI_STATUS_B0_MASK;
- if (new_status != priv->prev_status) {
- priv->diff_status |=
- new_status ^ priv->prev_status;
- wake_up_interruptible(&priv->delta_msr_wait);
- priv->prev_status = new_status;
- }
+ tty = tty_port_tty_get(&port->port);
+ if (!tty)
+ return;

- length = min_t(u32, priv->max_packet_size, urb->actual_length-packet_offset)-2;
- if (length < 0) {
- dev_err(&port->dev, "%s - bad packet length: %d\n",
- __func__, length+2);
- length = 0;
- }
+ /* FIXME: check priv? */

- if (priv->rx_flags & THROTTLED) {
- dbg("%s - throttled", __func__);
- break;
- }
- if (tty_buffer_request_room(tty, length) < length) {
- /* break out & wait for throttling/unthrottling to
- happen */
- dbg("%s - receive room low", __func__);
- break;
- }
+ for (i = 0; i < urb->actual_length; i += priv->max_packet_size) {
+ len = min_t(int, urb->actual_length - i, priv->max_packet_size);
+ count += ftdi_process_packet(tty, port, priv, &data[i], len);
+ }

- /* Handle errors and break */
- error_flag = TTY_NORMAL;
- /* Although the device uses a bitmask and hence can have
- multiple errors on a packet - the order here sets the
- priority the error is returned to the tty layer */
+ if (count)
+ tty_flip_buffer_push(tty);
+ tty_kref_put(tty);
+}

- if (data[packet_offset+1] & FTDI_RS_OE) {
- error_flag = TTY_OVERRUN;
- dbg("OVERRRUN error");
- }
- if (data[packet_offset+1] & FTDI_RS_BI) {
- error_flag = TTY_BREAK;
- dbg("BREAK received");
- usb_serial_handle_break(port);
- }
- if (data[packet_offset+1] & FTDI_RS_PE) {
- error_flag = TTY_PARITY;
- dbg("PARITY error");
- }
- if (data[packet_offset+1] & FTDI_RS_FE) {
- error_flag = TTY_FRAME;
- dbg("FRAMING error");
- }
- if (length > 0) {
- for (i = 2; i < length+2; i++) {
- /* Note that the error flag is duplicated for
- every character received since we don't know
- which character it applied to */
- if (!usb_serial_handle_sysrq_char(tty, port,
- data[packet_offset + i]))
- tty_insert_flip_char(tty,
- data[packet_offset + i],
- error_flag);
- }
- need_flip = 1;
- }
+static void ftdi_read_bulk_callback(struct urb *urb)
+{
+ struct usb_serial_port *port = urb->context;
+ unsigned char *data = urb->transfer_buffer;
+ int status = urb->status;
+ unsigned long flags;

-#ifdef NOT_CORRECT_BUT_KEEPING_IT_FOR_NOW
- /* if a parity error is detected you get status packets forever
- until a character is sent without a parity error.
- This doesn't work well since the application receives a
- never ending stream of bad data - even though new data
- hasn't been sent. Therefore I (bill) have taken this out.
- However - this might make sense for framing errors and so on
- so I am leaving the code in for now.
- */
- else {
- if (error_flag != TTY_NORMAL) {
- dbg("error_flag is not normal");
- /* In this case it is just status - if that is
- an error send a bad character */
- if (tty->flip.count >= TTY_FLIPBUF_SIZE)
- tty_flip_buffer_push(tty);
- tty_insert_flip_char(tty, 0xff, error_flag);
- need_flip = 1;
- }
- }
-#endif
- } /* "for(packet_offset=0..." */
+ dbg("%s - port %d", __func__, port->number);

- /* Low latency */
- if (need_flip)
- tty_flip_buffer_push(tty);
+ /* FIXME: remove? */
+ if (urb->number_of_packets > 0) {
+ dev_err(&port->dev, "%s transfer_buffer_length %d "
+ "actual_length %d number of packets %d\n", __func__,
+ urb->transfer_buffer_length,
+ urb->actual_length, urb->number_of_packets);
+ dev_err(&port->dev, "%s transfer_flags %x\n", __func__,
+ urb->transfer_flags);
+ }

- if (packet_offset < urb->actual_length) {
- /* not completely processed - record progress */
- priv->rx_processed = packet_offset;
- dbg("%s - incomplete, %d bytes processed, %d remain",
- __func__, packet_offset,
- urb->actual_length - packet_offset);
- /* check if we were throttled while processing */
- spin_lock_irqsave(&priv->rx_lock, flags);
- if (priv->rx_flags & THROTTLED) {
- priv->rx_flags |= ACTUALLY_THROTTLED;
- spin_unlock_irqrestore(&priv->rx_lock, flags);
- dbg("%s - deferring remainder until unthrottled",
- __func__);
- goto out;
- }
- spin_unlock_irqrestore(&priv->rx_lock, flags);
- /* if the port is closed stop trying to read */
- if (port->port.count > 0)
- /* delay processing of remainder */
- schedule_delayed_work(&priv->rx_work, 1);
- else
- dbg("%s - port is closed", __func__);
- goto out;
+ if (unlikely(status != 0)) {
+ dbg("%s - nonzero read bulk status received: %d",
+ __func__, status);
+ return;
}

- /* urb is completely processed */
- priv->rx_processed = 0;
+ /* FIXME: check urb != port->read_urb? */

- /* if the port is closed stop trying to read */
- if (port->port.count > 0) {
- /* Continue trying to always read */
- usb_fill_bulk_urb(port->read_urb, port->serial->dev,
- usb_rcvbulkpipe(port->serial->dev,
- port->bulk_in_endpointAddress),
- port->read_urb->transfer_buffer,
- port->read_urb->transfer_buffer_length,
- ftdi_read_bulk_callback, port);
+ usb_serial_debug_data(debug, &port->dev, __func__,
+ urb->actual_length, data);

- result = usb_submit_urb(port->read_urb, GFP_ATOMIC);
- if (result)
- dev_err(&port->dev,
- "%s - failed resubmitting read urb, error %d\n",
- __func__, result);
- }
-out:
- tty_kref_put(tty);
-} /* ftdi_process_read */
+ ftdi_process_read(port);

+ spin_lock_irqsave(&port->lock, flags);
+ port->throttled = port->throttle_req;
+ if (!port->throttled) {
+ spin_unlock_irqrestore(&port->lock, flags);
+ ftdi_submit_read_urb(port, GFP_ATOMIC);
+ } else
+ spin_unlock_irqrestore(&port->lock, flags);
+}

static void ftdi_break_ctl(struct tty_struct *tty, int break_state)
{
@@ -2605,33 +2469,30 @@ static int ftdi_ioctl(struct tty_struct *tty, struct file *file,
static void ftdi_throttle(struct tty_struct *tty)
{
struct usb_serial_port *port = tty->driver_data;
- struct ftdi_private *priv = usb_get_serial_port_data(port);
unsigned long flags;

dbg("%s - port %d", __func__, port->number);

- spin_lock_irqsave(&priv->rx_lock, flags);
- priv->rx_flags |= THROTTLED;
- spin_unlock_irqrestore(&priv->rx_lock, flags);
+ spin_lock_irqsave(&port->lock, flags);
+ port->throttle_req = 1;
+ spin_unlock_irqrestore(&port->lock, flags);
}

-
-static void ftdi_unthrottle(struct tty_struct *tty)
+void ftdi_unthrottle(struct tty_struct *tty)
{
struct usb_serial_port *port = tty->driver_data;
- struct ftdi_private *priv = usb_get_serial_port_data(port);
- int actually_throttled;
+ int was_throttled;
unsigned long flags;

dbg("%s - port %d", __func__, port->number);

- spin_lock_irqsave(&priv->rx_lock, flags);
- actually_throttled = priv->rx_flags & ACTUALLY_THROTTLED;
- priv->rx_flags &= ~(THROTTLED | ACTUALLY_THROTTLED);
- spin_unlock_irqrestore(&priv->rx_lock, flags);
+ spin_lock_irqsave(&port->lock, flags);
+ was_throttled = port->throttled;
+ port->throttled = port->throttle_req = 0;
+ spin_unlock_irqrestore(&port->lock, flags);

- if (actually_throttled)
- schedule_delayed_work(&priv->rx_work, 0);
+ if (was_throttled && !test_bit(ASYNCB_CLOSING, &port->port.flags))
+ ftdi_submit_read_urb(port, GFP_KERNEL);
}

static int __init ftdi_init(void)
--
1.6.4.2

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