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

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Message-ID: <CAOesGMhYLOZ8_hRmw7mY-2bTf65N-06g_YVm2fr-cnV=Y3widA@mail.gmail.com>
Date:   Tue, 20 Sep 2022 09:01:34 -0700
From:   Olof Johansson <olof@...om.net>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
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

On Mon, Sep 19, 2022 at 11:14 PM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> 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.

Yep, thanks for pointing that out. v2 sent out (after test).


-Olof