[PATCH 5.4 115/138] serial: tegra: fix CREAD handling for PIO

[Greg Kroah-Hartman]

From: Johan Hovold <johan@xxxxxxxxxx>

commit b374c562ee7ab3f3a1daf959c01868bae761571c upstream.

Commit 33ae787b74fc ("serial: tegra: add support to ignore read") added
support for dropping input in case CREAD isn't set, but for PIO the
ignore_status_mask wasn't checked until after the character had been
put in the receive buffer.

Note that the NULL tty-port test is bogus and will be removed by a
follow-on patch.

Fixes: 33ae787b74fc ("serial: tegra: add support to ignore read")
Cc: stable <stable@xxxxxxxxxxxxxxx>     # 5.4
Cc: Shardar Shariff Md <smohammed@xxxxxxxxxx>
Cc: Krishna Yarlagadda <kyarlagadda@xxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Acked-by: Thierry Reding <treding@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200710135947.2737-2-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/serial-tegra.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -651,11 +651,14 @@ static void tegra_uart_handle_rx_pio(str
 		ch = (unsigned char) tegra_uart_read(tup, UART_RX);
 		tup->uport.icount.rx++;
 
-		if (!uart_handle_sysrq_char(&tup->uport, ch) && tty)
-			tty_insert_flip_char(tty, ch, flag);
+		if (uart_handle_sysrq_char(&tup->uport, ch))
+			continue;
 
 		if (tup->uport.ignore_status_mask & UART_LSR_DR)
 			continue;
+
+		if (tty)
+			tty_insert_flip_char(tty, ch, flag);
 	} while (1);
 }