hwrng: bcm2835 - Manage an optional clock

One of the last steps before bcm63xx-rng can be eliminated is to manage
a clock during hwrng::init and hwrng::cleanup, so fetch it in the probe
function, and manage it during these two steps when valid.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/bcm2835-rng.c

@@ -15,6 +15,7 @@
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
 #include <linux/printk.h>
+#include <linux/clk.h>
 
 #define RNG_CTRL	0x0
 #define RNG_STATUS	0x4
@@ -33,6 +34,7 @@ struct bcm2835_rng_priv {
 	struct hwrng rng;
 	void __iomem *base;
 	bool mask_interrupts;
+	struct clk *clk;
 };
 
 static inline struct bcm2835_rng_priv *to_rng_priv(struct hwrng *rng)
@@ -66,8 +68,15 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
 static int bcm2835_rng_init(struct hwrng *rng)
 {
 	struct bcm2835_rng_priv *priv = to_rng_priv(rng);
+	int ret = 0;
 	u32 val;
 
+	if (!IS_ERR(priv->clk)) {
+		ret = clk_prepare_enable(priv->clk);
+		if (ret)
+			return ret;
+	}
+
 	if (priv->mask_interrupts) {
 		/* mask the interrupt */
 		val = readl(priv->base + RNG_INT_MASK);
@@ -79,7 +88,7 @@ static int bcm2835_rng_init(struct hwrng *rng)
 	__raw_writel(RNG_WARMUP_COUNT, priv->base + RNG_STATUS);
 	__raw_writel(RNG_RBGEN, priv->base + RNG_CTRL);
 
-	return 0;
+	return ret;
 }
 
 static void bcm2835_rng_cleanup(struct hwrng *rng)
@@ -88,6 +97,9 @@ static void bcm2835_rng_cleanup(struct hwrng *rng)
 
 	/* disable rng hardware */
 	__raw_writel(0, priv->base + RNG_CTRL);
+
+	if (!IS_ERR(priv->clk))
+		clk_disable_unprepare(priv->clk);
 }
 
 struct bcm2835_rng_of_data {
@@ -130,6 +142,9 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
 		return PTR_ERR(priv->base);
 	}
 
+	/* Clock is optional on most platforms */
+	priv->clk = devm_clk_get(dev, NULL);
+
 	priv->rng.name = "bcm2835-rng";
 	priv->rng.init = bcm2835_rng_init;
 	priv->rng.read = bcm2835_rng_read;