The baud clock is gated on some MediaTek SoCs and can be managed by
runtime power management.

Disable and unprepare the baud clock when suspending the UART, prepare
and enable it again when resuming it.

Fixes: e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock management")
Suggested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
v2: add this patch as suggested by AngeloGioacchino Del Regno in
https://lore.kernel.org/all/8b1c1796-6de2-4526-9a29-d8649141b878@collabora.com/ (local)

 drivers/tty/serial/8250/8250_mtk.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
index 9329ed1f759d..5875a7b9b4b1 100644
--- a/drivers/tty/serial/8250/8250_mtk.c
+++ b/drivers/tty/serial/8250/8250_mtk.c

@@ -435,6 +435,7 @@ static int __maybe_unused mtk8250_runtime_suspend(struct device *dev)
 	while
 		(serial_in(up, MTK_UART_DEBUG0));
 
+	clk_disable_unprepare(data->uart_clk);
 	clk_disable_unprepare(data->bus_clk);
 
 	return 0;

@@ -445,6 +446,7 @@ static int __maybe_unused mtk8250_runtime_resume(struct device *dev)
 	struct mtk8250_data *data = dev_get_drvdata(dev);
 
 	clk_prepare_enable(data->bus_clk);
+	clk_prepare_enable(data->uart_clk);
 
 	return 0;
 }

-- 
2.51.0