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USB: serial: ch341: fix baud rate and line-control handling

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commit 55fa15b598 upstream.

Revert to using direct register writes to set the divisor and
line-control registers.

A recent change switched to using the init vendor command to update
these registers, something which also enabled support for CH341A
devices. It turns out that simply setting bit 7 in the divisor register
is sufficient to support CH341A and specifically prevent data from being
buffered until a full endpoint-size packet (32 bytes) has been received.

Using the init command also had the side-effect of temporarily
deasserting the DTR/RTS signals on every termios change (including
initialisation on open) something which for example could cause problems
in setups where DTR is used to trigger a reset.

Fixes: 4e46c410e0 ("USB: serial: ch341: reinitialize chip on
reconfiguration")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Johan Hovold 2017-01-06 19:15:16 +01:00 committed by Ben Hutchings
parent f7eabb9350
commit 16ce3fcc77
1 changed files with 17 additions and 7 deletions
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24
drivers/usb/serial/ch341.c
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@ -133,8 +133,8 @@ static int ch341_control_in(struct usb_device *dev,
return r;
}
static int ch341_init_set_baudrate(struct usb_device *dev,
struct ch341_private *priv, unsigned ctrl)
static int ch341_set_baudrate_lcr(struct usb_device *dev,
struct ch341_private *priv, u8 lcr)
{
short a;
int r;
@ -159,9 +159,19 @@ static int ch341_init_set_baudrate(struct usb_device *dev,
factor = 0x10000 - factor;
a = (factor & 0xff00) | divisor;
/* 0x9c is "enable SFR_UART Control register and timer" */
r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT,
0x9c | (ctrl << 8), a | 0x80);
/*
* CH341A buffers data until a full endpoint-size packet (32 bytes)
* has been received unless bit 7 is set.
*/
a |= BIT(7);
r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x1312, a);
if (r)
return r;
r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x2518, lcr);
if (r)
return r;
return r;
}
@ -240,7 +250,7 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
if (r < 0)
goto out;
r = ch341_init_set_baudrate(dev, priv, 0);
r = ch341_set_baudrate_lcr(dev, priv, 0);
if (r < 0)
goto out;
@ -378,7 +388,7 @@ static void ch341_set_termios(struct tty_struct *tty,
if (baud_rate) {
priv->baud_rate = baud_rate;
r = ch341_init_set_baudrate(port->serial->dev, priv, ctrl);
r = ch341_set_baudrate_lcr(port->serial->dev, priv, ctrl);
if (r < 0 && old_termios) {
priv->baud_rate = tty_termios_baud_rate(old_termios);
tty_termios_copy_hw(tty->termios, old_termios);