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References: <20200128110102.11522-1-martin@kaiser.cx> <20200128110102.11522-4-martin@kaiser.cx>
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From:   PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Date:   Wed, 12 Feb 2020 21:43:55 +0530
Message-ID: <CANc+2y6Scy1=S7zeQ4gVowRoWmzsq4wiNXbLVeY1Qvu0oo9cUw@mail.gmail.com>
Subject: Re: [PATCH 3/6] hwrng: imx-rngc - use devres for registration
To:     Martin Kaiser <martin@kaiser.cx>
Cc:     Herbert Xu <herbert@gondor.apana.org.au>,
        NXP Linux Team <linux-imx@nxp.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        open list <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Martin,

On Tue, 28 Jan 2020 at 16:31, Martin Kaiser <martin@kaiser.cx> wrote:
>
> Use devres to register the rngc with the hwrng core. Drop the explicit
> deregistration.
>
> Signed-off-by: Martin Kaiser <martin@kaiser.cx>
> ---
>  drivers/char/hw_random/imx-rngc.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/char/hw_random/imx-rngc.c b/drivers/char/hw_random/imx-rngc.c
> index 903894518c8d..1381ddd5b891 100644
> --- a/drivers/char/hw_random/imx-rngc.c
> +++ b/drivers/char/hw_random/imx-rngc.c
> @@ -263,7 +263,7 @@ static int imx_rngc_probe(struct platform_device *pdev)
>                 }
>         }
>
> -       ret = hwrng_register(&rngc->rng);
> +       ret = devm_hwrng_register(&pdev->dev, &rngc->rng);
>         if (ret) {
>                 dev_err(&pdev->dev, "FSL RNGC registering failed (%d)\n", ret);
>                 goto err;
> @@ -282,8 +282,6 @@ static int __exit imx_rngc_remove(struct platform_device *pdev)
>  {
>         struct imx_rngc *rngc = platform_get_drvdata(pdev);
>
> -       hwrng_unregister(&rngc->rng);
> -
>         clk_disable_unprepare(rngc->clk);
>
>         return 0;
> --
> 2.20.1
>

After imx_rngc_remove function hwrng_unregister will get called. This
leaves a window where the clock to rng hardware block is disabled but
still user space can access it via /dev/hwrng. This does not look
right, please revisit the patch.

Regards,
PrasannaKumar