hwrng: stm32 - allow disable clock error detection

Add a new property that allow to disable the clock error
detection which is required when the clock source selected
is out of specification (which is not mandatory).
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/stm32-rng.c

@@ -26,6 +26,7 @@
 
 #define RNG_CR 0x00
 #define RNG_CR_RNGEN BIT(2)
+#define RNG_CR_CED BIT(5)
 
 #define RNG_SR 0x04
 #define RNG_SR_SEIS BIT(6)
@@ -48,6 +49,7 @@ struct stm32_rng_private {
 	void __iomem *base;
 	struct clk *clk;
 	struct reset_control *rst;
+	bool ced;
 };
 
 static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
@@ -101,7 +103,11 @@ static int stm32_rng_init(struct hwrng *rng)
 	if (err)
 		return err;
 
-	writel_relaxed(RNG_CR_RNGEN, priv->base + RNG_CR);
+	if (priv->ced)
+		writel_relaxed(RNG_CR_RNGEN, priv->base + RNG_CR);
+	else
+		writel_relaxed(RNG_CR_RNGEN | RNG_CR_CED,
+			       priv->base + RNG_CR);
 
 	/* clear error indicators */
 	writel_relaxed(0, priv->base + RNG_SR);
@@ -149,6 +155,8 @@ static int stm32_rng_probe(struct platform_device *ofdev)
 		reset_control_deassert(priv->rst);
 	}
 
+	priv->ced = of_property_read_bool(np, "clock-error-detect");
+
 	dev_set_drvdata(dev, priv);
 
 	priv->rng.name = dev_driver_string(dev),