hwrng: bcm2835 - add reset support

BCM6368 devices need to reset the IPSEC controller 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>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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)
@@ -92,6 +94,10 @@ static int bcm2835_rng_init(struct hwrng *rng)
 	if (ret)
 		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);
@@ -156,6 +162,10 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
 	if (IS_ERR(priv->clk))
 		return PTR_ERR(priv->clk);
 
+	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;