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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 <ldewangan@nvidia.com>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
hifive-unleashed-5.1
Stephen Warren 2011-05-17 16:12:37 -06:00 committed by Greg Kroah-Hartman
parent 4539c24fe4
commit 5f873bae70
2 changed files with 29 additions and 0 deletions
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28
drivers/tty/serial/8250.c
View File

@ -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

1
include/linux/serial_reg.h
View File

@ -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 */