tty/serial: atmel: Prevent a warning on suspend

The atmel serial port driver reported the following warning on suspend:
atmel_usart f8020000.serial: ttyS1: Unable to drain transmitter

As the ATMEL_US_TXEMPTY status bit in ATMEL_US_CSR is always cleared
when the transmitter is disabled, we need to know the transmitter's
state to return the real fifo state. And as ATMEL_US_CR is write-only,
it is necessary to save the state of the transmitter in a local
variable, and update the variable when TXEN and TXDIS is written in
ATMEL_US_CR.

After those changes, atmel_tx_empty can return "empty" on suspend, the
warning in uart_suspend_port disappears, and suspending is 20ms shorter
for each enabled Atmel serial port.

Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 04e55f0..82d9c8e 100644 (file)
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -171,6 +171,7 @@ struct atmel_uart_port {
        bool                    has_hw_timer;
        struct timer_list       uart_timer;
 
+       bool                    tx_stopped;
        bool                    suspended;
        unsigned int            pending;
        unsigned int            pending_status;
@@ -380,6 +381,10 @@ static int atmel_config_rs485(struct uart_port *port,
  */
 static u_int atmel_tx_empty(struct uart_port *port)
 {
+       struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
+
+       if (atmel_port->tx_stopped)
+               return TIOCSER_TEMT;
        return (atmel_uart_readl(port, ATMEL_US_CSR) & ATMEL_US_TXEMPTY) ?
                TIOCSER_TEMT :
                0;
@@ -485,6 +490,7 @@ static void atmel_stop_tx(struct uart_port *port)
         * is fully transmitted.
         */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);
+       atmel_port->tx_stopped = true;
 
        /* Disable interrupts */
        atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
@@ -521,6 +527,7 @@ static void atmel_start_tx(struct uart_port *port)
 
        /* re-enable the transmitter */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
+       atmel_port->tx_stopped = false;
 }
 
 /*
@@ -1843,6 +1850,7 @@ static int atmel_startup(struct uart_port *port)
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
        /* enable xmit & rcvr */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
+       atmel_port->tx_stopped = false;
 
        setup_timer(&atmel_port->uart_timer,
                        atmel_uart_timer_callback,
@@ -2099,6 +2107,7 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 
        /* disable receiver and transmitter */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS | ATMEL_US_RXDIS);
+       atmel_port->tx_stopped = true;
 
        /* mode */
        if (port->rs485.flags & SER_RS485_ENABLED) {
@@ -2184,6 +2193,7 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
        atmel_uart_writel(port, ATMEL_US_BRGR, quot);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
+       atmel_port->tx_stopped = false;
 
        /* restore interrupts */
        atmel_uart_writel(port, ATMEL_US_IER, imr);
@@ -2427,6 +2437,7 @@ static void atmel_console_write(struct console *co, const char *s, u_int count)
 
        /* Make sure that tx path is actually able to send characters */
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
+       atmel_port->tx_stopped = false;
 
        uart_console_write(port, s, count, atmel_console_putchar);
 
@@ -2488,6 +2499,7 @@ static int __init atmel_console_setup(struct console *co, char *options)
 {
        int ret;
        struct uart_port *port = &atmel_ports[co->index].uart;
+       struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
        int baud = 115200;
        int bits = 8;
        int parity = 'n';
@@ -2505,6 +2517,7 @@ static int __init atmel_console_setup(struct console *co, char *options)
        atmel_uart_writel(port, ATMEL_US_IDR, -1);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
        atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
+       atmel_port->tx_stopped = false;
 
        if (options)
                uart_parse_options(options, &baud, &parity, &bits, &flow);