linux-kernel - Re: [PATCH] tty: serial: 8250

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Message-ID: <8b1c1796-6de2-4526-9a29-d8649141b878@collabora.com>
Date: Mon, 15 Sep 2025 09:33:46 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Daniel Golle <daniel@...rotopia.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, Matthias Brugger
 <matthias.bgg@...il.com>, Yu Jiaoliang <yujiaoliang@...o.com>,
 Uwe Kleine-König <u.kleine-koenig@...libre.com>,
 Changqi Hu <changqi.hu@...iatek.com>, Sam Shih <sam.shih@...iatek.com>,
 Steven Liu <steven.liu@...iatek.com>, John Crispin <john@...ozen.org>,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] tty: serial: 8250_mtk: enable baud clock

Il 14/09/25 01:59, 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 as enabled to prevent disabling it
> among with the unused clocks.
> Runtime power management can probably also be restored to the state before
> commit e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock
> management"), but that isn't strictly needed to fix the regression
> introduced by that commit.
> 
> Fixes: e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock management")
> Suggested-by: Sam Shih <sam.shih@...iatek.com>
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>

Is there any particular reason why you didn't en/disable the uart_clk in
runtime PM ops?

Cheers,
Angelo

> ---
>   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);