Hi Stephan,

On 18 August 2017 at 00:22, Stephan Mueller [off-list ref] wrote:

Am Donnerstag, 17. August 2017, 20:25:17 CEST schrieb PrasannaKumar
Muralidharan:

Hi PrasannaKumar,

quoted

+
+static int jz4780_rng_generate(struct crypto_rng *tfm,
+                            const u8 *src, unsigned int slen,
+                            u8 *dst, unsigned int dlen)
+{
+     struct jz4780_rng_ctx *ctx = crypto_rng_ctx(tfm);
+     struct jz4780_rng *rng = ctx->rng;
+     u32 data;
+
+     /*
+      * JZ4780 Programmers manual says the RNG should not run continuously
+      * for more than 1s. So enable RNG, read data and disable it.
+      * NOTE: No issue was observed with MIPS creator CI20 board even when
+      * RNG ran continuously for longer periods. This is just a precaution.
+      *
+      * A delay is required so that the current RNG data is not bit shifted
+      * version of previous RNG data which could happen if random data is
+      * read continuously from this device.
+      */
+     jz4780_rng_writel(rng, 1, REG_RNG_CTRL);
+     do {
+             data = jz4780_rng_readl(rng, REG_RNG_DATA);
+             memcpy((void *)dst, (void *)&data, 4);

How do you know that dst is a multiple of 4 bytes? When dlen is only 3, you
overflow the buffer.

You are right. I initially used hw_random framework for this driver.
But later realised that PRNG driver should use crypto framework. When
I started using crypto I reused most of the code. This was because of
porting. Will change it and send next version.

quoted

+             dlen -= 4;
+             dst += 4;
+             udelay(20);
+     } while (dlen >= 4);
+
+     if (dlen > 0) {
+             data = jz4780_rng_readl(rng, REG_RNG_DATA);
+             memcpy((void *)dst, (void *)&data, dlen);
+     }
+     jz4780_rng_writel(rng, 0, REG_RNG_CTRL);
+
+     return 0;
+}

Ciao
Stephan

Thanks,
PrasannaKumar