serial: 8250_mtk: Enable baud clock and manage in runtime PM

commit d518314a1fa4e980a227d1b2bda1badf433cb932 upstream.

Some MediaTek SoCs got a gated UART baud clock, which currently gets
disabled as the clk subsystem believes it would be unused. This results in
the uart freezing right after "clk: Disabling unused clocks" on those
platforms.

Request the baud clock to be prepared and enabled during probe, and to
restore run-time power management capabilities to what it was before commit
e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock
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")
Fixes: b6c7ff2693ddc ("serial: 8250_mtk: Simplify clock sequencing and runtime PM")
Cc: stable <stable@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/de5197ccc31e1dab0965cabcc11ca92e67246cf6.1758058441.git.daniel@makrotopia.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
index b9cca210e171c38498677bb913cada8a924914c1..1c878986fcec0f735325e900a35b3aa4acdf5f6b 100644 (file)
--- 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;
 }
@@ -475,13 +477,13 @@ static int mtk8250_probe_of(struct platform_device *pdev, struct uart_port *p,
        int dmacnt;
 #endif
 
-       data->uart_clk = devm_clk_get(&pdev->dev, "baud");
+       data->uart_clk = devm_clk_get_enabled(&pdev->dev, "baud");
        if (IS_ERR(data->uart_clk)) {
                /*
                 * For compatibility with older device trees try unnamed
                 * clk when no baud clk can be found.
                 */
-               data->uart_clk = devm_clk_get(&pdev->dev, NULL);
+               data->uart_clk = devm_clk_get_enabled(&pdev->dev, NULL);
                if (IS_ERR(data->uart_clk)) {
                        dev_warn(&pdev->dev, "Can't get uart clock\n");
                        return PTR_ERR(data->uart_clk);