[PATCH 4.19 138/168] USB: serial: cp210x: re-enable auto-RTS on open

Greg Kroah-Hartman
2020-08-17T17:35:23Z

From: Brant Merryman <brant.merryman@silabs.com>

commit c7614ff9b73a1e6fb2b1b51396da132ed22fecdb upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/serial/cp210x.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -893,6 +893,7 @@ static void cp210x_get_termios_port(stru
u32 baud;
u16 bits;
u32 ctl_hs;
+ u32 flow_repl;

cp210x_read_u32_reg(port, CP210X_GET_BAUDRATE, &baud);

@@ -993,6 +994,22 @@ static void cp210x_get_termios_port(stru
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__);