The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From c7614ff9b73a1e6fb2b1b51396da132ed22fecdb Mon Sep 17 00:00:00 2001
From: Brant Merryman brant.merryman@silabs.com Date: Fri, 26 Jun 2020 04:24:20 +0000 Subject: [PATCH] USB: serial: cp210x: re-enable auto-RTS on open
CP210x hardware disables auto-RTS but leaves auto-CTS when in hardware flow control mode and UART on cp210x hardware is disabled. When re-opening the port, if auto-CTS is enabled on the cp210x, then auto-RTS must be re-enabled in the driver.
Signed-off-by: Brant Merryman brant.merryman@silabs.com Co-developed-by: Phu Luu phu.luu@silabs.com Signed-off-by: Phu Luu phu.luu@silabs.com Link: https://lore.kernel.org/r/ECCF8E73-91F3-4080-BE17-1714BC8818FB@silabs.com [ johan: fix up tags and problem description ] Fixes: 39a66b8d22a3 ("[PATCH] USB: CP2101 Add support for flow control") Cc: stable stable@vger.kernel.org # 2.6.12 Signed-off-by: Johan Hovold johan@kernel.org
diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c index bcceb4ad8be0..a90801ef0055 100644 --- a/drivers/usb/serial/cp210x.c +++ b/drivers/usb/serial/cp210x.c @@ -917,6 +917,7 @@ static void cp210x_get_termios_port(struct usb_serial_port *port, u32 baud; u16 bits; u32 ctl_hs; + u32 flow_repl;
cp210x_read_u32_reg(port, CP210X_GET_BAUDRATE, &baud);
@@ -1017,6 +1018,22 @@ static void cp210x_get_termios_port(struct usb_serial_port *port, ctl_hs = le32_to_cpu(flow_ctl.ulControlHandshake); if (ctl_hs & CP210X_SERIAL_CTS_HANDSHAKE) { dev_dbg(dev, "%s - flow control = CRTSCTS\n", __func__); + /* + * When the port is closed, the CP210x hardware disables + * auto-RTS and RTS is deasserted but it leaves auto-CTS when + * in hardware flow control mode. When re-opening the port, if + * auto-CTS is enabled on the cp210x, then auto-RTS must be + * re-enabled in the driver. + */ + flow_repl = le32_to_cpu(flow_ctl.ulFlowReplace); + flow_repl &= ~CP210X_SERIAL_RTS_MASK; + flow_repl |= CP210X_SERIAL_RTS_SHIFT(CP210X_SERIAL_RTS_FLOW_CTL); + flow_ctl.ulFlowReplace = cpu_to_le32(flow_repl); + cp210x_write_reg_block(port, + CP210X_SET_FLOW, + &flow_ctl, + sizeof(flow_ctl)); + cflag |= CRTSCTS; } else { dev_dbg(dev, "%s - flow control = NONE\n", __func__);