From 3af08bd7adb09b0806c51c06b87db08cc7075568 Mon Sep 17 00:00:00 2001 From: Russell King Date: Fri, 5 Oct 2012 13:32:08 +0100 Subject: [PATCH] SERIAL: omap: fix hardware assisted flow control When the UART device has hardware flow control enabled, it ignores the MCR RTS bit in the MCR register, and keeps RTS asserted as long as we continue to read characters from the UART receiver FIFO. This means that when the TTY buffers become full, the UART doesn't tell the remote end to stop sending, which causes the TTY layer to start dropping characters. A similar problem exists with software flow control. We need the FIFO register to fill when software flow control is enabled to provoke the UART to send the XOFF character. Fix this by implementing the throttle/unthrottle callbacks, and use these to disable receiver interrupts. This in turn means that the UART FIFO will fill, which will then cause the UART's hardware to deassert the RTS signal and/or send the XOFF character, stopping the remote end. Signed-off-by: Russell King --- drivers/tty/serial/omap-serial.c | 53 +++++++++++++++++++++++++------- 1 file changed, 42 insertions(+), 11 deletions(-) diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c index 156a85438558..4dbbc00c8266 100644 --- a/drivers/tty/serial/omap-serial.c +++ b/drivers/tty/serial/omap-serial.c @@ -88,10 +88,10 @@ #define OMAP_UART_WER_MOD_WKUP 0X7F /* Enable XON/XOFF flow control on output */ -#define OMAP_UART_SW_TX 0x4 +#define OMAP_UART_SW_TX 0x08 /* Enable XON/XOFF flow control on input */ -#define OMAP_UART_SW_RX 0x4 +#define OMAP_UART_SW_RX 0x02 #define OMAP_UART_SW_CLR 0xF0 @@ -354,6 +354,34 @@ static void serial_omap_start_tx(struct uart_port *port) pm_runtime_put_autosuspend(up->dev); } +static void serial_omap_throttle(struct uart_port *port) +{ + struct uart_omap_port *up = to_uart_omap_port(port); + unsigned long flags; + + pm_runtime_get_sync(up->dev); + spin_lock_irqsave(&up->port.lock, flags); + up->ier &= ~(UART_IER_RLSI | UART_IER_RDI); + serial_out(up, UART_IER, up->ier); + spin_unlock_irqrestore(&up->port.lock, flags); + pm_runtime_mark_last_busy(up->dev); + pm_runtime_put_autosuspend(up->dev); +} + +static void serial_omap_unthrottle(struct uart_port *port) +{ + struct uart_omap_port *up = to_uart_omap_port(port); + unsigned long flags; + + pm_runtime_get_sync(up->dev); + spin_lock_irqsave(&up->port.lock, flags); + up->ier |= UART_IER_RLSI | UART_IER_RDI; + serial_out(up, UART_IER, up->ier); + spin_unlock_irqrestore(&up->port.lock, flags); + pm_runtime_mark_last_busy(up->dev); + pm_runtime_put_autosuspend(up->dev); +} + static unsigned int check_modem_status(struct uart_omap_port *up) { unsigned int status; @@ -929,20 +957,20 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios, /* * IXON Flag: - * Enable XON/XOFF flow control on output. - * Transmit XON1, XOFF1 - */ - if (termios->c_iflag & IXON) - up->efr |= OMAP_UART_SW_TX; - - /* - * IXOFF Flag: * Enable XON/XOFF flow control on input. * Receiver compares XON1, XOFF1. */ - if (termios->c_iflag & IXOFF) + if (termios->c_iflag & IXON) up->efr |= OMAP_UART_SW_RX; + /* + * IXOFF Flag: + * Enable XON/XOFF flow control on output. + * Transmit XON1, XOFF1 + */ + if (termios->c_iflag & IXOFF) + up->efr |= OMAP_UART_SW_TX; + /* * IXANY Flag: * Enable any character to restart output. @@ -1025,6 +1053,7 @@ static void serial_omap_config_port(struct uart_port *port, int flags) dev_dbg(up->port.dev, "serial_omap_config_port+%d\n", up->port.line); up->port.type = PORT_OMAP; + up->port.flags |= UPF_SOFT_FLOW | UPF_HARD_FLOW; } static int @@ -1228,6 +1257,8 @@ static struct uart_ops serial_omap_pops = { .get_mctrl = serial_omap_get_mctrl, .stop_tx = serial_omap_stop_tx, .start_tx = serial_omap_start_tx, + .throttle = serial_omap_throttle, + .unthrottle = serial_omap_unthrottle, .stop_rx = serial_omap_stop_rx, .enable_ms = serial_omap_enable_ms, .break_ctl = serial_omap_break_ctl,