[PATCH v2 1/2] tty: serial: 8250_mtk: enable baud clock

[PATCH v2 1/2] tty: serial: 8250_mtk: enable baud clock

[Daniel Golle]

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.

To fix this request the baud clock to be prepared and enabled during probe.

Fixes: e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock management")
Suggested-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
v2: no changes

 drivers/tty/serial/8250/8250_mtk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
index b44de2ed7413..9329ed1f759d 100644
--- a/drivers/tty/serial/8250/8250_mtk.c
+++ b/drivers/tty/serial/8250/8250_mtk.c
@@ -475,13 +475,13 @@ 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);
-- 
2.51.0

[PATCH v2 2/2] tty: serial: 8250_mtk: manage baud clock in runtime PM ops

[Daniel Golle]

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/

 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

Re: [PATCH v2 1/2] tty: serial: 8250_mtk: enable baud clock

[AngeloGioacchino Del Regno]

Il 15/09/25 15:06, Daniel Golle ha scritto:
> 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.
> 
> To fix this request the baud clock to be prepared and enabled during probe.
> 
> Fixes: e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock management")
> Suggested-by: Sam Shih <sam.shih@mediatek.com>
> Signed-off-by: Daniel Golle <daniel@makrotopia.org>

Thanks for caring about power management. However, this and the addition in PM ops
should be a single commit. It's even using the same Fixes tag...! :-)

I've read both of the commits in this series and the code LGTM.


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

Please, squash the two commits, after which...

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

Cheers,
Angelo

> ---
> v2: no changes
> 
>   drivers/tty/serial/8250/8250_mtk.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
> index b44de2ed7413..9329ed1f759d 100644
> --- a/drivers/tty/serial/8250/8250_mtk.c
> +++ b/drivers/tty/serial/8250/8250_mtk.c
> @@ -475,13 +475,13 @@ 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);

Re: [PATCH v2 1/2] tty: serial: 8250_mtk: enable baud clock

[Andy Shevchenko]

On Mon, Sep 15, 2025 at 03:41:25PM +0200, AngeloGioacchino Del Regno wrote:
> Il 15/09/25 15:06, Daniel Golle ha scritto:

...

> I've read both of the commits in this series and the code LGTM.
> 
> tty: serial: 8250_mtk: Enable baud clock and manage in runtime PM

"tty: " part is not needed.

> Please, squash the two commits, after which...

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 1/2] tty: serial: 8250_mtk: enable baud clock

[Andy Shevchenko]

On Mon, Sep 15, 2025 at 02:06:37PM +0100, Daniel Golle wrote:

...

> -		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);

Consider making this to be either dev_warn_once() / _ratelimited() or
better to have

	return dev_err_probe(...);

This will allow to avoid flooding the logs when clock is not yet ready.
The proposed change can be done in the separate patch.

-- 
With Best Regards,
Andy Shevchenko