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Date: Thu, 16 May 2024 10:12:55 +0200
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Subject: Re: [PATCH 1/2] hwrng: stm32 - use pm_runtime_resume_and_get()
To: Marek Vasut <marex@denx.de>, <linux-crypto@vger.kernel.org>
CC: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Herbert Xu
	<herbert@gondor.apana.org.au>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Olivia Mackall <olivia@selenic.com>, Rob Herring <robh@kernel.org>,
        Yang
 Yingliang <yangyingliang@huawei.com>,
        <kernel@dh-electronics.com>, <linux-arm-kernel@lists.infradead.org>,
        <linux-stm32@st-md-mailman.stormreply.com>
References: <20240516012210.128307-1-marex@denx.de>
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From: Gatien CHEVALLIER <gatien.chevallier@foss.st.com>
In-Reply-To: <20240516012210.128307-1-marex@denx.de>
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On 5/16/24 03:20, Marek Vasut wrote:
> include/linux/pm_runtime.h pm_runtime_get_sync() description suggests to
> ... consider using pm_runtime_resume_and_get() instead of it, especially
> if its return value is checked by the caller, as this is likely to result
> in cleaner code.
> 
> This is indeed better, switch to pm_runtime_resume_and_get() which
> correctly suspends the device again in case of failure. Also add error
> checking into the RNG driver in case pm_runtime_resume_and_get() does
> fail, which is currently not done, and it does detect sporadic -EACCES
> error return after resume, which would otherwise lead to a hang due to
> register access on un-resumed hardware. Now the read simply errors out
> and the system does not hang.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
> Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
> Cc: Gatien Chevallier <gatien.chevallier@foss.st.com>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: Marek Vasut <marex@denx.de>
> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> Cc: Olivia Mackall <olivia@selenic.com>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Yang Yingliang <yangyingliang@huawei.com>
> Cc: kernel@dh-electronics.com
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-crypto@vger.kernel.org
> Cc: linux-stm32@st-md-mailman.stormreply.com
> ---
>   drivers/char/hw_random/stm32-rng.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
> index 0e903d6e22e30..6dec4adc49853 100644
> --- a/drivers/char/hw_random/stm32-rng.c
> +++ b/drivers/char/hw_random/stm32-rng.c
> @@ -187,7 +187,9 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
>   	int retval = 0, err = 0;
>   	u32 sr;
>   
> -	pm_runtime_get_sync((struct device *) priv->rng.priv);
> +	retval = pm_runtime_resume_and_get((struct device *)priv->rng.priv);
> +	if (retval)
> +		return retval;
>   
>   	if (readl_relaxed(priv->base + RNG_SR) & RNG_SR_SEIS)
>   		stm32_rng_conceal_seed_error(rng);

Hi Marek,

I'll check in other stm32 drivers as well.

Acked-by: Gatien Chevallier <gatien.chevallier@foss.st.com>

Thanks,
Gatien