Am Samstag, 25. M?rz 2017, 17:26:52 CEST schrieb Krzysztof Kozlowski:

Hi Krzysztof,

+static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
+			       const u8 *seed, unsigned int slen)
+{
+	u32 val;
+	int i;
+
+	dev_dbg(rng->dev, "Seeding with %u bytes\n", slen);
+
+	if (slen < EXYNOS_RNG_SEED_SIZE) {
+		dev_warn(rng->dev, "Seed too short (only %u bytes)\n", slen);
+		return -EINVAL;
+	}
+
+	for (i = 0 ; i < EXYNOS_RNG_SEED_REGS ; i++) {
+		val = seed[i * 4] << 24;
+		val |= seed[i * 4 + 1] << 16;
+		val |= seed[i * 4 + 2] << 8;
+		val |= seed[i * 4 + 3] << 0;
+
+		exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(i));
+	}

Would it make sense to add another outer loop here to allow all of slen to be 
injected into the DRNG? Note, in some cases, a user wants to add more seed 
into the DRNG than the actual seed size. In this case, the DRNG acts as a 
compression operation of entropy. This is used when the entropy-to-data ratio 
is not 1:1. In a lot of cases, users have a seed which has less entropy in 
bits per data bit.

Ciao
Stephan