linux-kernel - Re: [PATCH] serial: sifive: enable clocks for UART when probed

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Date:   Tue, 20 Sep 2022 08:14:34 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Olof Johansson <olof@...om.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH] serial: sifive: enable clocks for UART when probed

Hello,

On Mon, Sep 19, 2022 at 03:39:15PM -0700, Olof Johansson wrote:
> When the PWM driver was changed to disable clocks if no PWMs are enabled,
> it ended up also disabling the shared parent with the UART, since the
> UART doesn't do any clock enablement on its own.
> 
> To avoid these surprises, add clk_prepare_enable/clk_disable_unprepare
> calls.
> 
> Fixes: ace41d7564e655 ("pwm: sifive: Ensure the clk is enabled exactly once per running PWM")
> Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Cc: Emil Renner Berthing <emil.renner.berthing@...onical.com>
> Cc: Palmer Dabbelt <palmer@...belt.com>
> Cc: Paul Walmsley <paul.walmsley@...ive.com>
> Signed-off-by: Olof Johansson <olof@...om.net>
> ---
>  drivers/tty/serial/sifive.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/serial/sifive.c b/drivers/tty/serial/sifive.c
> index 5c3a07546a58..751f98068806 100644
> --- a/drivers/tty/serial/sifive.c
> +++ b/drivers/tty/serial/sifive.c
> @@ -950,23 +950,28 @@ static int sifive_serial_probe(struct platform_device *pdev)
>  		dev_err(&pdev->dev, "unable to find controller clock\n");
>  		return PTR_ERR(clk);
>  	}
> +	clk_prepare_enable(clk);

The return code of clk_prepare_enable() must be checked. Also there is a
simpler patch to fix that problem. I didn't test but I expect just doing 

diff --git a/drivers/tty/serial/sifive.c b/drivers/tty/serial/sifive.c
index 5c3a07546a58..4b1d4fe8458e 100644
--- a/drivers/tty/serial/sifive.c
+++ b/drivers/tty/serial/sifive.c
@@ -945,7 +945,7 @@ static int sifive_serial_probe(struct platform_device *pdev)
 		return PTR_ERR(base);
 	}
 
-	clk = devm_clk_get(&pdev->dev, NULL);
+	clk = devm_clk_get_enabled(&pdev->dev, NULL);
 	if (IS_ERR(clk)) {
 		dev_err(&pdev->dev, "unable to find controller clock\n");
 		return PTR_ERR(clk);

would be enough and also cares for disabling the clock on remove.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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