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

From: Johan Hovold
Date: Sat Oct 03 2009 - 07:42:43 EST

On Fri, Oct 02, 2009 at 05:33:08PM +0100, Alan Cox wrote:
> For upstream how does this look as a tidy up

I found a couple of issues:

- The patch breaks unthrottling, as it checks THROTTLE before resubmitting
urb whereas unthrottle checks ACTUALLY_UNTROTTLED which is never set.

- The countread stuff should also be removed from
ftdi_read_bulk_callback as they where only used for updating
rx_bytes,

And, obviously, this doesn't solve the problem of tty_flip_buffer_push
being called from interrupt context (but I assume that was never the
intention).


I've actually been working on cleaning up ftdi_sio inspired by the
generic driver. I also threw out the work queue, but had not noticed the
unused rx_byte yet. I also used the generic drivers scheme of not
pushing to tty until unthrottled, but as you point out this is not really
needed anymore.

My patch is quite large, and could be split up once finished.

With the removal of low_latency patch it solves the remaining issues at
hand with ftdi_sio:

- It does not stall when a read callback is made during serial_open.
- It handles the late call to unthrottle during serial_open.

What do you think?

Thanks,
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 | 425 ++++++++++++++---------------------------
1 files changed, 142 insertions(+), 283 deletions(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 0ac2c2f..a7c76df 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 +1727,13 @@ 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;
+ 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 +1779,6 @@ 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 +2001,141 @@ static int ftdi_chars_in_buffer(struct tty_struct *tty)
return buffered;
}

-static void ftdi_read_bulk_callback(struct urb *urb)
+static void 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;
+ /* 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;
}

- priv = usb_get_serial_port_data(port);
- if (!priv) {
- dbg("%s - bad port private data pointer - exiting", __func__);
- 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");
}
-
- 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;
+ if (packet[1] & FTDI_RS_BI) {
+ flag = TTY_BREAK;
+ dbg("BREAK received");
+ usb_serial_handle_break(port);
+ }
+ if (packet[1] & FTDI_RS_PE) {
+ flag = TTY_PARITY;
+ dbg("PARITY error");
+ }
+ if (packet[1] & FTDI_RS_FE) {
+ flag = TTY_FRAME;
+ dbg("FRAMING 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 */
+ /*
+ * 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.
+ */
+ ch = packet + 2;
+ len -= 2;
+ if (!port->console || !port->sysrq)
+ tty_insert_flip_string(tty, ch, len);
+ else {
+ /* Push data to tty */
+ for (i = 0; i < len; i++, ch++) {
+ if (!usb_serial_handle_sysrq_char(tty, port, *ch))
+ tty_insert_flip_char(tty, *ch, flag);
+ }
+ }
+}


-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;
+static void ftdi_process_read(struct usb_serial_port *port)
+{
+ struct urb *urb = port->read_urb;
struct tty_struct *tty;
- char error_flag;
- unsigned char *data;
-
+ struct ftdi_private *priv = usb_get_serial_port_data(port);
+ char *data = (char *)urb->transfer_buffer;
int i;
- int result;
+ int len;
int need_flip;
- int packet_offset;
- unsigned long flags;

- dbg("%s - port %d", __func__, port->number);
-
- if (port->port.count <= 0)
- return;
+ if (urb->actual_length <= 2)
+ return; /* status only */

- tty = tty_port_tty_get(&port->port);
- if (!tty) {
- dbg("%s - bad tty pointer - exiting", __func__);
+ tty = tty_port_tty_get(&port->port);
+ if (!tty)
return;
- }

- priv = usb_get_serial_port_data(port);
- if (!priv) {
- dbg("%s - bad port private data pointer - exiting", __func__);
- goto out;
- }
-
- urb = port->read_urb;
- if (!urb) {
- dbg("%s - bad read_urb pointer - exiting", __func__);
- goto out;
- }
-
- 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]);
- }
-
-
- /* 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;
- }
+ /* FIXME: check priv? */

- 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;
- }
-
- 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;
- }
-
- /* 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 (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);
- }
+ for (i = 0; i < urb->actual_length; i += priv->max_packet_size) {
+ len = min_t(int, urb->actual_length - i, priv->max_packet_size);
+ if (len > 2) {
+ ftdi_process_packet(tty, port, priv, &data[i], len);
need_flip = 1;
}
+ }

-#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..." */
-
- /* Low latency */
if (need_flip)
tty_flip_buffer_push(tty);
+ tty_kref_put(tty);
+}

- 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;
- }
+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;

- /* urb is completely processed */
- priv->rx_processed = 0;
+ dbg("%s - port %d", __func__, port->number);

- /* 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);
+ /* 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);
+ }

- 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);
+ if (unlikely(status != 0)) {
+ dbg("%s - nonzero read bulk status received: %d",
+ __func__, status);
+ return;
}
-out:
- tty_kref_put(tty);
-} /* ftdi_process_read */

+ /* FIXME: check urb != port->read_urb? */
+
+ usb_serial_debug_data(debug, &port->dev, __func__,
+ urb->actual_length, data);
+
+ ftdi_process_read(port);
+
+ spin_lock_irqsave(&port->lock, flags);
+ 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 +2467,30 @@ 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->throttled = 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 = 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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