bcm2835-rng: Avoid initialising if already enabled

raspberrypi inclusion
category: feature
bugzilla: 50432

--------------------------------

Avoids the 0x40000 cycles of warmup again if firmware has already used it
Signed-off-by: NFang Yafen <yafen@iscas.ac.cn>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/char/hw_random/bcm2835-rng.c

@@ -102,8 +102,10 @@ static int bcm2835_rng_init(struct hwrng *rng)
 	}
 
 	/* set warm-up count & enable */
-	rng_writel(priv, RNG_WARMUP_COUNT, RNG_STATUS);
-	rng_writel(priv, RNG_RBGEN, RNG_CTRL);
+	if (!(rng_readl(priv, RNG_CTRL) & RNG_RBGEN)) {
+		rng_writel(priv, RNG_WARMUP_COUNT, RNG_STATUS);
+		rng_writel(priv, RNG_RBGEN, RNG_CTRL);
+	}
 
 	return ret;
 }