Am Samstag, 25. März 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