From 5f873bae704cf8b7cbd64b5720912266286c9146 Mon Sep 17 00:00:00 2001 From: Stephen Warren Date: Tue, 17 May 2011 16:12:37 -0600 Subject: [PATCH] tty/serial: Fix break handling for PORT_TEGRA When a break is received, Tegra's UART apparently fills the FIFO with 0 bytes. These must be drained so that they aren't interpreted as actual data received. This allows e.g. MAGIC_SYSRQ to work on Tegra's UARTs. v2: Added FIXME comment to clear_rx_fifo Originally-by: Laxman Dewangan Cc: Laxman Dewangan Signed-off-by: Stephen Warren Acked-by: Alan Cox Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250.c | 28 ++++++++++++++++++++++++++++ include/linux/serial_reg.h | 1 + 2 files changed, 29 insertions(+) diff --git a/drivers/tty/serial/8250.c b/drivers/tty/serial/8250.c index a5e290de8c93..b40f7b90c81d 100644 --- a/drivers/tty/serial/8250.c +++ b/drivers/tty/serial/8250.c @@ -1433,6 +1433,27 @@ static void serial8250_enable_ms(struct uart_port *port) serial_out(up, UART_IER, up->ier); } +/* + * Clear the Tegra rx fifo after a break + * + * FIXME: This needs to become a port specific callback once we have a + * framework for this + */ +static void clear_rx_fifo(struct uart_8250_port *up) +{ + unsigned int status, tmout = 10000; + do { + status = serial_in(up, UART_LSR); + if (status & (UART_LSR_FIFOE | UART_LSR_BRK_ERROR_BITS)) + status = serial_in(up, UART_RX); + else + break; + if (--tmout == 0) + break; + udelay(1); + } while (1); +} + static void receive_chars(struct uart_8250_port *up, unsigned int *status) { @@ -1467,6 +1488,13 @@ receive_chars(struct uart_8250_port *up, unsigned int *status) if (lsr & UART_LSR_BI) { lsr &= ~(UART_LSR_FE | UART_LSR_PE); up->port.icount.brk++; + /* + * If tegra port then clear the rx fifo to + * accept another break/character. + */ + if (up->port.type == PORT_TEGRA) + clear_rx_fifo(up); + /* * We do the SysRQ and SAK checking * here because otherwise the break diff --git a/include/linux/serial_reg.h b/include/linux/serial_reg.h index 5f66e8499fb9..c75bda37c18e 100644 --- a/include/linux/serial_reg.h +++ b/include/linux/serial_reg.h @@ -119,6 +119,7 @@ #define UART_MCR_DTR 0x01 /* DTR complement */ #define UART_LSR 5 /* In: Line Status Register */ +#define UART_LSR_FIFOE 0x80 /* Fifo error */ #define UART_LSR_TEMT 0x40 /* Transmitter empty */ #define UART_LSR_THRE 0x20 /* Transmit-hold-register empty */ #define UART_LSR_BI 0x10 /* Break interrupt indicator */ -- 2.39.5