Excerpts from Paul Mackerras's message of June 18, 2021 1:47 pm:
> Microwatt's hardware RNG is accessed using the DARN instruction.
>
I think we're getting a platforms/book3s soon with the VAS patches,
might be a place to add the get_random_darn function.
Huh, DARN is unprivileged right? And yet we haven't wired it up in
pseries it still uses an hcall.
Anyway that's all stuff to sort out later.
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> Signed-off-by: Paul Mackerras <pau...@ozlabs.org>
> ---
> arch/powerpc/platforms/microwatt/Kconfig | 1 +
> arch/powerpc/platforms/microwatt/Makefile | 2 +-
> arch/powerpc/platforms/microwatt/rng.c | 48 +++++++++++++++++++++++
> 3 files changed, 50 insertions(+), 1 deletion(-)
> create mode 100644 arch/powerpc/platforms/microwatt/rng.c
>
> diff --git a/arch/powerpc/platforms/microwatt/Kconfig
> b/arch/powerpc/platforms/microwatt/Kconfig
> index 50ed0cedb5f1..8f6a81978461 100644
> --- a/arch/powerpc/platforms/microwatt/Kconfig
> +++ b/arch/powerpc/platforms/microwatt/Kconfig
> @@ -7,6 +7,7 @@ config PPC_MICROWATT
> select PPC_ICP_NATIVE
> select PPC_NATIVE
> select PPC_UDBG_16550
> + select ARCH_RANDOM
> help
> This option enables support for FPGA-based Microwatt
> implementations.
>
> diff --git a/arch/powerpc/platforms/microwatt/Makefile
> b/arch/powerpc/platforms/microwatt/Makefile
> index e6885b3b2ee7..116d6d3ad3f0 100644
> --- a/arch/powerpc/platforms/microwatt/Makefile
> +++ b/arch/powerpc/platforms/microwatt/Makefile
> @@ -1 +1 @@
> -obj-y += setup.o
> +obj-y += setup.o rng.o
> diff --git a/arch/powerpc/platforms/microwatt/rng.c
> b/arch/powerpc/platforms/microwatt/rng.c
> new file mode 100644
> index 000000000000..3d8ee6eb7dad
> --- /dev/null
> +++ b/arch/powerpc/platforms/microwatt/rng.c
> @@ -0,0 +1,48 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Derived from arch/powerpc/platforms/powernv/rng.c, which is:
> + * Copyright 2013, Michael Ellerman, IBM Corporation.
> + */
> +
> +#define pr_fmt(fmt) "microwatt-rng: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/smp.h>
> +#include <asm/archrandom.h>
> +#include <asm/cputable.h>
> +#include <asm/machdep.h>
> +
> +#define DARN_ERR 0xFFFFFFFFFFFFFFFFul
> +
> +int microwatt_get_random_darn(unsigned long *v)
> +{
> + unsigned long val;
> +
> + /* Using DARN with L=1 - 64-bit conditioned random number */
> + asm volatile(PPC_DARN(%0, 1) : "=r"(val));
> +
> + if (val == DARN_ERR)
> + return 0;
> +
> + *v = val;
> +
> + return 1;
> +}
> +
> +static __init int rng_init(void)
> +{
> + unsigned long val;
> + int i;
> +
> + for (i = 0; i < 10; i++) {
> + if (microwatt_get_random_darn(&val)) {
> + ppc_md.get_random_seed = microwatt_get_random_darn;
> + return 0;
> + }
> + }
> +
> + pr_warn("Unable to use DARN for get_random_seed()\n");
> +
> + return -EIO;
> +}
> +machine_subsys_initcall(, rng_init);
> --
> 2.31.1
>
>
