[PATCH v3] serial: 8250_mtk: Enable baud clock and manage in runtime PM

[Daniel Golle]

On Wed, Sep 17, 2025 at 12:00:57PM +0200, Matthias Brugger wrote:
> On 16/09/2025 23:37, Daniel Golle wrote:
> > 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")
> 
> Most of the issues from this commit are already fixed in
> b6c7ff2693ddc ("serial: 8250_mtk: Simplify clock sequencing and runtime PM")
> which is more or less a revert of e32a83c70cf9.
> 
> I think we should add
> Fixes: b6c7ff2693ddc ("serial: 8250_mtk: Simplify clock sequencing and runtime PM")
> here as well. It's a fix of a fix :)

Just a friendly ping about this patch :)
Should I resend the patch with the added Fixes:-tag? Or can it be merged
including the tag added my Matthias without a resend?


> 
> Regards,
> Matthias
> 
> 
> > Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
> > Signed-off-by: Daniel Golle <daniel at makrotopia.org>
> > ---
> > v3: squash into single patch
> > v2: add managing run-time PM in dedicated patch
> > 
> >   drivers/tty/serial/8250/8250_mtk.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
> > index b44de2ed7413..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;
> >   }
> > @@ -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);
>