linux-kernel - Re: [PATCH v4 1/2] hwrng: imx-rngc: Use optional clock

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Message-ID: <CAMuHMdUGmw+Pa43oqcGzt0x7ED2FGw0=U7XddvdaUZ3GFmsxsQ@mail.gmail.com>
Date: Thu, 27 Nov 2025 09:37:05 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Martin Kaiser <martin@...ser.cx>
Cc: Jean-Michel Hautbois via B4 Relay <devnull+jeanmichel.hautbois.yoseli.org@...nel.org>, 
	Greg Ungerer <gerg@...ux-m68k.org>, Olivia Mackall <olivia@...enic.com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, linux-m68k@...ts.linux-m68k.org, 
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org, 
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>, Frank Li <Frank.Li@....com>
Subject: Re: [PATCH v4 1/2] hwrng: imx-rngc: Use optional clock

Hi Martin,

On Wed, 26 Nov 2025 at 21:30, Martin Kaiser <martin@...ser.cx> wrote:
> Thus wrote Jean-Michel Hautbois via B4 Relay (devnull+jeanmichel.hautbois.yoseli.org@...nel.org):
>
> > From: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
>
> > Change devm_clk_get() to devm_clk_get_optional() to support platforms
> > where the RNG clock is always enabled and not exposed via the clock
> > framework (such as ColdFire MCF54418).
>
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
> > ---
> >  drivers/char/hw_random/imx-rngc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> > diff --git a/drivers/char/hw_random/imx-rngc.c b/drivers/char/hw_random/imx-rngc.c
> > index 241664a9b5d9..d6a847e48339 100644
> > --- a/drivers/char/hw_random/imx-rngc.c
> > +++ b/drivers/char/hw_random/imx-rngc.c
> > @@ -259,7 +259,7 @@ static int __init imx_rngc_probe(struct platform_device *pdev)
> >       if (IS_ERR(rngc->base))
> >               return PTR_ERR(rngc->base);
>
> > -     rngc->clk = devm_clk_get(&pdev->dev, NULL);
> > +     rngc->clk = devm_clk_get_optional(&pdev->dev, NULL);
> >       if (IS_ERR(rngc->clk))
> >               return dev_err_probe(&pdev->dev, PTR_ERR(rngc->clk), "Cannot get rng_clk\n");
>
> The clock is not optional on a standard imx25 system. If it's missing in the
> device tree, the rngb will not work and we should not load the driver.

As the clocks property is marked required in
Documentation/devicetree/bindings/rng/imx-rng.yaml, "make dtbs_check"
should flag a missing clock.

> Should we call devm_clk_get or devm_clk_get_optional, depending on the
> detected device?

That can quickly lead to complex code.  Nowadays it is fine to rely on
"make dtbs_check" for some part of the validation.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds