From 409cc4541ade015acd11f2566dcda599363a87a3 Mon Sep 17 00:00:00 2001 From: Andrij Abyzov Date: Mon, 28 Sep 2020 16:41:27 +0200 Subject: [PATCH] serial: 8250_fsl: Fix TX interrupt handling condition This is the port of the commit db1b5bc047b3 ("serial: 8250: Fix TX interrupt handling condition") to the 8250_fsl irq handling logic. 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 check if THRI is set in IER in addition of the TX fifo status. THRI in IER is set when TX is started and cleared when TX is stopped. This ensures that TX handling is only called when there is really transmission on going and an interrupt for THRE and not when there are only RX interrupts. Signed-off-by: Andrij Abyzov Link: https://lore.kernel.org/r/20200928144127.87156-1-aabyzov@slb.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_fsl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index c3582d8938d6..fbcc90c31ca1 100644 --- a/drivers/tty/serial/8250/8250_fsl.c +++ b/drivers/tty/serial/8250/8250_fsl.c @@ -78,7 +78,7 @@ int fsl8250_handle_irq(struct uart_port *port) serial8250_modem_status(up); - if (lsr & UART_LSR_THRE) + if ((lsr & UART_LSR_THRE) && (up->ier & UART_IER_THRI)) serial8250_tx_chars(up); up->lsr_saved_flags = orig_lsr; -- 2.20.1