[SERIAL] Add explaination why we don't use RTS flow control.

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 7232f14f3d594466f2f240aa5cda4fbcf380682d..e8b24bc57774f4b4cbb28d1f28581cf21617cad7 100644 (file)
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1658,9 +1658,17 @@ serial8250_set_termios(struct uart_port *port, struct termios *termios,
        serial_out(up, UART_IER, up->ier);
 
        if (up->capabilities & UART_CAP_EFR) {
+               unsigned char efr = 0;
+               /*
+                * TI16C752/Startech hardware flow control.  FIXME:
+                * - TI16C752 requires control thresholds to be set.
+                * - UART_MCR_RTS is ineffective if auto-RTS mode is enabled.
+                */
+               if (termios->c_cflag & CRTSCTS)
+                       efr |= UART_EFR_CTS;
+
                serial_outp(up, UART_LCR, 0xBF);
-               serial_outp(up, UART_EFR,
-                           termios->c_cflag & CRTSCTS ? UART_EFR_CTS :0);
+               serial_outp(up, UART_EFR, efr);
        }
 
        if (up->capabilities & UART_NATSEMI) {