From: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Date: Thu, 28 May 2020 17:47:47 +0200
Subject: tty: serial: imx: clear Ageing Timer Interrupt in handler
Git-commit: d1d996afbd2bca3bf3c484fc1f7a738134d65207
Patch-mainline: v5.8-rc1
References: jsc#SLE-16106

The AGTIM flag must be cleared explicitly, otherwise the IRQ handler
will be called in an endless loop.

Fortunately, this issue currently doesn't affect mainline kernels in
practice, as the the RX FIFO trigger level is set to 1 in UFCR. When
setting the trigger level to a higher number, the issue is trivially
reproducible by any RX without DMA that doesn't fill the FIFO up to the
configured level.

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Link: https://lore.kernel.org/r/20200528154747.14201-1-matthias.schiffer@ew.tq-group.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---
 drivers/tty/serial/imx.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 6b078e395931..1265e8d86d8a 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -909,6 +909,8 @@ static irqreturn_t imx_uart_int(int irq, void *dev_id)
 		usr2 &= ~USR2_ORE;
 
 	if (usr1 & (USR1_RRDY | USR1_AGTIM)) {
+		imx_uart_writel(sport, USR1_AGTIM, USR1);
+
 		__imx_uart_rxint(irq, dev_id);
 		ret = IRQ_HANDLED;
 	}