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[PATCH] USB: ftdi_sio: Update RTS and DTR simultaneously
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ftdi_sio: Update RTS and DTR simultaneously, using a single control URB
instead of separate control URBs for RTS and DTR.  Reinhard Bergmann
observed time differences of up to 680 ms with his application on a
2.4.22 kernel when RTS and DTR were updated using separate control
URBs, which is unacceptable.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Ian Abbott authored and Linus Torvalds committed Jul 29, 2005
1 parent 9b1513d commit 74ede0f
Showing 1 changed file with 43 additions and 95 deletions.
138 changes: 43 additions & 95 deletions drivers/usb/serial/ftdi_sio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -596,62 +596,59 @@ static __u32 ftdi_232bm_baud_to_divisor(int baud)
return(ftdi_232bm_baud_base_to_divisor(baud, 48000000));
}

static int set_rts(struct usb_serial_port *port, int high_or_low)
#define set_mctrl(port, set) update_mctrl((port), (set), 0)
#define clear_mctrl(port, clear) update_mctrl((port), 0, (clear))

static int update_mctrl(struct usb_serial_port *port, unsigned int set, unsigned int clear)
{
struct ftdi_private *priv = usb_get_serial_port_data(port);
char *buf;
unsigned ftdi_high_or_low;
unsigned urb_value;
int rv;

buf = kmalloc(1, GFP_NOIO);
if (!buf)
return -ENOMEM;

if (high_or_low) {
ftdi_high_or_low = FTDI_SIO_SET_RTS_HIGH;
priv->last_dtr_rts |= TIOCM_RTS;
} else {
ftdi_high_or_low = FTDI_SIO_SET_RTS_LOW;
priv->last_dtr_rts &= ~TIOCM_RTS;
}
rv = usb_control_msg(port->serial->dev,
usb_sndctrlpipe(port->serial->dev, 0),
FTDI_SIO_SET_MODEM_CTRL_REQUEST,
FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE,
ftdi_high_or_low, priv->interface,
buf, 0, WDR_TIMEOUT);

kfree(buf);
return rv;
}

if (((set | clear) & (TIOCM_DTR | TIOCM_RTS)) == 0) {
dbg("%s - DTR|RTS not being set|cleared", __FUNCTION__);
return 0; /* no change */
}

static int set_dtr(struct usb_serial_port *port, int high_or_low)
{
struct ftdi_private *priv = usb_get_serial_port_data(port);
char *buf;
unsigned ftdi_high_or_low;
int rv;

buf = kmalloc(1, GFP_NOIO);
if (!buf)
if (!buf) {
return -ENOMEM;

if (high_or_low) {
ftdi_high_or_low = FTDI_SIO_SET_DTR_HIGH;
priv->last_dtr_rts |= TIOCM_DTR;
} else {
ftdi_high_or_low = FTDI_SIO_SET_DTR_LOW;
priv->last_dtr_rts &= ~TIOCM_DTR;
}

clear &= ~set; /* 'set' takes precedence over 'clear' */
urb_value = 0;
if (clear & TIOCM_DTR)
urb_value |= FTDI_SIO_SET_DTR_LOW;
if (clear & TIOCM_RTS)
urb_value |= FTDI_SIO_SET_RTS_LOW;
if (set & TIOCM_DTR)
urb_value |= FTDI_SIO_SET_DTR_HIGH;
if (set & TIOCM_RTS)
urb_value |= FTDI_SIO_SET_RTS_HIGH;
rv = usb_control_msg(port->serial->dev,
usb_sndctrlpipe(port->serial->dev, 0),
FTDI_SIO_SET_MODEM_CTRL_REQUEST,
FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE,
ftdi_high_or_low, priv->interface,
urb_value, priv->interface,
buf, 0, WDR_TIMEOUT);

kfree(buf);
if (rv < 0) {
err("%s Error from MODEM_CTRL urb: DTR %s, RTS %s",
__FUNCTION__,
(set & TIOCM_DTR) ? "HIGH" :
(clear & TIOCM_DTR) ? "LOW" : "unchanged",
(set & TIOCM_RTS) ? "HIGH" :
(clear & TIOCM_RTS) ? "LOW" : "unchanged");
} else {
dbg("%s - DTR %s, RTS %s", __FUNCTION__,
(set & TIOCM_DTR) ? "HIGH" :
(clear & TIOCM_DTR) ? "LOW" : "unchanged",
(set & TIOCM_RTS) ? "HIGH" :
(clear & TIOCM_RTS) ? "LOW" : "unchanged");
priv->last_dtr_rts = (priv->last_dtr_rts & ~clear) | set;
}
return rv;
}

Expand Down Expand Up @@ -1222,12 +1219,7 @@ static int ftdi_open (struct usb_serial_port *port, struct file *filp)
/* FIXME: Flow control might be enabled, so it should be checked -
we have no control of defaults! */
/* Turn on RTS and DTR since we are not flow controlling by default */
if (set_dtr(port, HIGH) < 0) {
err("%s Error from DTR HIGH urb", __FUNCTION__);
}
if (set_rts(port, HIGH) < 0){
err("%s Error from RTS HIGH urb", __FUNCTION__);
}
set_mctrl(port, TIOCM_DTR | TIOCM_RTS);

/* Not throttled */
spin_lock_irqsave(&priv->rx_lock, flags);
Expand Down Expand Up @@ -1277,14 +1269,8 @@ static void ftdi_close (struct usb_serial_port *port, struct file *filp)
err("error from flowcontrol urb");
}

/* drop DTR */
if (set_dtr(port, LOW) < 0){
err("Error from DTR LOW urb");
}
/* drop RTS */
if (set_rts(port, LOW) < 0) {
err("Error from RTS LOW urb");
}
/* drop RTS and DTR */
clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
} /* Note change no line if hupcl is off */

/* cancel any scheduled reading */
Expand Down Expand Up @@ -1815,25 +1801,14 @@ static void ftdi_set_termios (struct usb_serial_port *port, struct termios *old_
err("%s error from disable flowcontrol urb", __FUNCTION__);
}
/* Drop RTS and DTR */
if (set_dtr(port, LOW) < 0){
err("%s Error from DTR LOW urb", __FUNCTION__);
}
if (set_rts(port, LOW) < 0){
err("%s Error from RTS LOW urb", __FUNCTION__);
}

clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
} else {
/* set the baudrate determined before */
if (change_speed(port)) {
err("%s urb failed to set baurdrate", __FUNCTION__);
}
/* Ensure RTS and DTR are raised */
else if (set_dtr(port, HIGH) < 0){
err("%s Error from DTR HIGH urb", __FUNCTION__);
}
else if (set_rts(port, HIGH) < 0){
err("%s Error from RTS HIGH urb", __FUNCTION__);
}
set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
}

/* Set flow control */
Expand Down Expand Up @@ -1945,35 +1920,8 @@ static int ftdi_tiocmget (struct usb_serial_port *port, struct file *file)

static int ftdi_tiocmset(struct usb_serial_port *port, struct file * file, unsigned int set, unsigned int clear)
{
int ret;

dbg("%s TIOCMSET", __FUNCTION__);
if (set & TIOCM_DTR){
if ((ret = set_dtr(port, HIGH)) < 0) {
err("Urb to set DTR failed");
return(ret);
}
}
if (set & TIOCM_RTS) {
if ((ret = set_rts(port, HIGH)) < 0){
err("Urb to set RTS failed");
return(ret);
}
}

if (clear & TIOCM_DTR){
if ((ret = set_dtr(port, LOW)) < 0){
err("Urb to unset DTR failed");
return(ret);
}
}
if (clear & TIOCM_RTS) {
if ((ret = set_rts(port, LOW)) < 0){
err("Urb to unset RTS failed");
return(ret);
}
}
return(0);
return update_mctrl(port, set, clear);
}


Expand Down

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