4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vignesh R <vigneshr@xxxxxx>
[ Upstream commit 2e9fe539108320820016f78ca7704a7342788380 ]
Currently, data in RX FIFO is read based on UART_LSR register state even
if RDI and RLSI interrupts are disabled in UART_IER register.
This is because when IRQ handler is called due to TX FIFO empty event,
RX FIFO is serviced based on UART_LSR register status instead of
UART_IIR status. This defeats the purpose of disabling UART RX
FIFO interrupts during throttling(see, omap_8250_throttle()) as IRQ
handler continues to drain UART RX FIFO resulting in overflow of buffer
at tty layer.
Fix this by making sure that driver drains UART RX FIFO only when
UART_IIR_RDI is set along with UART_LSR_BI or UART_LSR_DR bits.
Signed-off-by: Vignesh R <vigneshr@xxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_port.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1874,7 +1874,8 @@ int serial8250_handle_irq(struct uart_po
status = serial_port_in(port, UART_LSR);
- if (status & (UART_LSR_DR | UART_LSR_BI)) {
+ if (status & (UART_LSR_DR | UART_LSR_BI) &&
+ iir & UART_IIR_RDI) {
if (!up->dma || handle_rx_dma(up, iir))
status = serial8250_rx_chars(up, status);
}
