[PATCH v4 2/2] hwrng: bcm2835: add reset support

Álvaro Fernández Rojas
2021-02-24T08:24:10Z

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

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
v4: add reset_control_rearm().
v3: no changes.
v2: no changes.

drivers/char/hw_random/bcm2835-rng.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
index 1a7c43b43c6b..92658edaff22 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;
+
if (priv->mask_interrupts) {
/* mask the interrupt */
val = rng_readl(priv, RNG_INT_MASK);
@@ -115,6 +121,8 @@ static void bcm2835_rng_cleanup(struct hwrng *rng)
/* disable rng hardware */
rng_writel(priv, 0, RNG_CTRL);

+ reset_control_rearm(priv->reset);
+
if (!IS_ERR(priv->clk))
clk_disable_unprepare(priv->clk);
}
@@ -159,6 +167,10 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
if (PTR_ERR(priv->clk) == -EPROBE_DEFER)
return -EPROBE_DEFER;

+ priv->reset = devm_reset_control_get_optional_exclusive(dev, NULL);
+ if (IS_ERR(priv->reset))
+ return PTR_ERR(priv->reset);
+
priv->rng.name = pdev->name;
priv->rng.init = bcm2835_rng_init;
priv->rng.read = bcm2835_rng_read;
--
2.20.1