serial: 8250: Auto CTS control by HW if AFE enabled

According to DesignWare 8250 spec, if auto flow control
mode is enabled, a change in CTS does not cause an interrupt,
so sw-assisted CTS flow control mode will not work properly.

There reported an GPS firmware download failure issue, and we
verified the root cause is, the default sw-assisted CTS flow
control mode can not work properly since no interrupt when got
CTS signal.

This patch is to enable auto CTS mode by defaut if CRTSCTS
is enable for DesignWare 8250 controller.

Signed-off-by: Huiquan Zhong <huiquan.zhong@intel.com>
Signed-off-by: Qipeng Zha <qipeng.zha@intel.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index d48b506..8d04ea7 100644 (file)
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -257,6 +257,11 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
 
        if (!ret)
                p->uartclk = rate;
+
+       p->status &= ~UPSTAT_AUTOCTS;
+       if (termios->c_cflag & CRTSCTS)
+               p->status |= UPSTAT_AUTOCTS;
+
 out:
        serial8250_do_set_termios(p, termios, old);
 }

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index df2e61e..dd4483f 100644 (file)
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -1417,6 +1417,10 @@ byt_set_termios(struct uart_port *p, struct ktermios *termios,
        reg |= BYT_PRV_CLK_EN | BYT_PRV_CLK_UPDATE;
        writel(reg, p->membase + BYT_PRV_CLK);
 
+       p->status &= ~UPSTAT_AUTOCTS;
+       if (termios->c_cflag & CRTSCTS)
+               p->status |= UPSTAT_AUTOCTS;
+
        serial8250_do_set_termios(p, termios, old);
 }