1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Derived from arch/powerpc/platforms/powernv/rng.c, which is:
4  * Copyright 2013, Michael Ellerman, IBM Corporation.
5  */
6 
7 #define pr_fmt(fmt)	"microwatt-rng: " fmt
8 
9 #include <linux/kernel.h>
10 #include <linux/smp.h>
11 #include <asm/archrandom.h>
12 #include <asm/cputable.h>
13 #include <asm/machdep.h>
14 
15 #define DARN_ERR 0xFFFFFFFFFFFFFFFFul
16 
17 static int microwatt_get_random_darn(unsigned long *v)
18 {
19 	unsigned long val;
20 
21 	/* Using DARN with L=1 - 64-bit conditioned random number */
22 	asm volatile(PPC_DARN(%0, 1) : "=r"(val));
23 
24 	if (val == DARN_ERR)
25 		return 0;
26 
27 	*v = val;
28 
29 	return 1;
30 }
31 
32 static __init int rng_init(void)
33 {
34 	unsigned long val;
35 	int i;
36 
37 	for (i = 0; i < 10; i++) {
38 		if (microwatt_get_random_darn(&val)) {
39 			ppc_md.get_random_seed = microwatt_get_random_darn;
40 			return 0;
41 		}
42 	}
43 
44 	pr_warn("Unable to use DARN for get_random_seed()\n");
45 
46 	return -EIO;
47 }
48 machine_subsys_initcall(, rng_init);
49