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

Florian Fainelli
2021-02-23T20:44:37Z

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@OpenWrt:/# 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@gmail.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