u-boot/net/net_rand.h

/*
 *	Copied from LiMon - BOOTP.
 *
 *	Copyright 1994, 1995, 2000 Neil Russell.
 *	(See License)
 *	Copyright 2000 Paolo Scaffardi
 */

#ifndef __NET_RAND_H__
#define __NET_RAND_H__

#include <dm/uclass.h>
#include <rng.h>

/*
 * Return a seed for the PRNG derived from the eth0 MAC address.
 */
static inline unsigned int seed_mac(void)
{
	unsigned char enetaddr[ARP_HLEN];
	unsigned int seed;

	/* get our mac */
	memcpy(enetaddr, eth_get_ethaddr(), ARP_HLEN);

	seed = enetaddr[5];
	seed ^= enetaddr[4] << 8;
	seed ^= enetaddr[3] << 16;
	seed ^= enetaddr[2] << 24;
	seed ^= enetaddr[1];
	seed ^= enetaddr[0] << 8;

	return seed;
}

/*
 * Seed the random number generator using the eth0 MAC address.
 */
static inline void srand_mac(void)
{
	int ret;
	struct udevice *devp;
	u32 randv = 0;

	if (IS_ENABLED(CONFIG_DM_RNG)) {
		ret = uclass_get_device(UCLASS_RNG, 0, &devp);
		if (ret) {
			ret = dm_rng_read(devp, &randv, sizeof(randv));
			if (ret < 0)
				randv = 0;
		}
	}
	if (randv)
		srand(randv);
	else
		srand(seed_mac());
}

#endif /* __NET_RAND_H__ */