On Fri, Apr 26, 2019 at 12:06:13PM +0000, Rautkoski Kimmo EXT wrote: > 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..91ca0ca 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_THRI)) > serial8250_tx_chars(up); This feels wrong to me, can someone else test this to verify that it really does work properly? I don't have access to any 8250 devices at the moment :( thanks, greg k-h
