3.16.42-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Johan Hovold <johan@xxxxxxxxxx> commit 55fa15b5987db22b4f35d3f0798928c126be5f1c 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: 4e46c410e050 ("USB: serial: ch341: reinitialize chip on reconfiguration") Signed-off-by: Johan Hovold <johan@xxxxxxxxxx> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- drivers/usb/serial/ch341.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) --- a/drivers/usb/serial/ch341.c +++ b/drivers/usb/serial/ch341.c @@ -132,8 +132,8 @@ static int ch341_control_in(struct usb_d 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; @@ -156,9 +156,19 @@ static int ch341_init_set_baudrate(struc 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; } @@ -231,7 +241,7 @@ static int ch341_configure(struct usb_de 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; @@ -366,7 +376,7 @@ static void ch341_set_termios(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);