Interrupt handler checked THRE bit (transmitter holding register empty) in LSR to detect if TX fifo is empty. In case when there is only receive interrupts the TX handling got called because THRE bit in LSR is set when there is no transmission (FIFO empty). TX handling caused TX stop, which in RS-485 half-duplex mode actually resets receiver FIFO. This is not desired during reception because of possible data loss. The fix is to use IIR instead of LSR to detect the TX fifo status. This ensures that TX handling is only called when there is really an interrupt for THRE and not when there is only RX interrupts. Signed-off-by: Kimmo Rautkoski <ext-kimmo.rautkoski@xxxxxxxxxxx> --- drivers/tty/serial/8250/8250_port.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index d2f3310..989dbac 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1875,7 +1875,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) status = serial8250_rx_chars(up, status); } serial8250_modem_status(up); - if ((!up->dma || up->dma->tx_err) && (status & UART_LSR_THRE)) + if ((!up->dma || up->dma->tx_err) && ((iir & UART_IIR_ID) == UART_IIR_THRI)) serial8250_tx_chars(up); uart_unlock_and_check_sysrq(port, flags); -- 2.1.4
