linux-kernel - Re: [PATCH v3 2/2] hwrng: bcm2835: add reset support

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Date:   Tue, 23 Feb 2021 12:43:32 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Álvaro Fernández Rojas <noltari@...il.com>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Rob Herring <robh+dt@...nel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Mark Brown <broonie@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Nícolas F. R. A. Prado 
        <nfraprado@...tonmail.com>,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        linux-crypto@...r.kernel.org, devicetree@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] hwrng: bcm2835: add reset support



On 2/23/2021 9:00 AM, Álvaro Fernández Rojas wrote:
> BCM6368 devices need to reset the in order to generate true random numbers.
> This is what BCM6368 produces without a reset:
> root@...nWrt:/# cat /dev/hwrng | rngtest -c 1000
> rngtest 6.10
> Copyright (c) 2004 by Henrique de Moraes Holschuh
> This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> 
> rngtest: starting FIPS tests...
> rngtest: bits received from input: 20000032
> rngtest: FIPS 140-2 successes: 0
> rngtest: FIPS 140-2 failures: 1000
> rngtest: FIPS 140-2(2001-10-10) Monobit: 2
> rngtest: FIPS 140-2(2001-10-10) Poker: 1000
> rngtest: FIPS 140-2(2001-10-10) Runs: 1000
> rngtest: FIPS 140-2(2001-10-10) Long run: 30
> rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
> rngtest: input channel speed: (min=37.253; avg=320.827; max=635.783)Mibits/s
> rngtest: FIPS tests speed: (min=12.141; avg=15.034; max=16.428)Mibits/s
> rngtest: Program run time: 1336176 microseconds
> cat: write error: Broken pipe
> 
> Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> ---
>  v3: no changes.
>  v2: no changes.
> 
>  drivers/char/hw_random/bcm2835-rng.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
> index 1a7c43b43c6b..1b93a896d8e8 100644
> --- a/drivers/char/hw_random/bcm2835-rng.c
> +++ b/drivers/char/hw_random/bcm2835-rng.c
> @@ -13,6 +13,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/printk.h>
>  #include <linux/clk.h>
> +#include <linux/reset.h>
>  
>  #define RNG_CTRL	0x0
>  #define RNG_STATUS	0x4
> @@ -32,6 +33,7 @@ struct bcm2835_rng_priv {
>  	void __iomem *base;
>  	bool mask_interrupts;
>  	struct clk *clk;
> +	struct reset_control *reset;
>  };
>  
>  static inline struct bcm2835_rng_priv *to_rng_priv(struct hwrng *rng)
> @@ -94,6 +96,10 @@ static int bcm2835_rng_init(struct hwrng *rng)
>  			return ret;
>  	}
>  
> +	ret = reset_control_reset(priv->reset);
> +	if (ret)
> +		return ret;

For symmetry, the remove path should call reset_control_rearm(),
assuming that .reset() is what you want and not .deassert()/assert().
-- 
Florian