cmd: add rng command

For the RNG uclass we currently only have a test working on the sandbox.

Provide a command to test the hardware random number generator on
non-sandbox systems.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

cmd/Kconfig

@@ -1672,6 +1672,13 @@ config CMD_GETTIME
 	  milliseconds. See also the 'bootstage' command which provides more
 	  flexibility for boot timing.
 
+config CMD_RNG
+	bool "rng command"
+	depends on DM_RNG
+	select HEXDUMP
+	help
+	  Print bytes from the hardware random number generator.
+
 # TODO: rename to CMD_SLEEP
 config CMD_MISC
 	bool "sleep"

cmd/Makefile

@@ -117,6 +117,7 @@ obj-$(CONFIG_CMD_READ) += read.o
 obj-$(CONFIG_CMD_REGINFO) += reginfo.o
 obj-$(CONFIG_CMD_REISER) += reiser.o
 obj-$(CONFIG_CMD_REMOTEPROC) += remoteproc.o
+obj-$(CONFIG_CMD_RNG) += rng.o
 obj-$(CONFIG_CMD_ROCKUSB) += rockusb.o
 obj-$(CONFIG_SANDBOX) += host.o
 obj-$(CONFIG_CMD_SATA) += sata.o

cmd/rng.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * The 'rng' command prints bytes from the hardware random number generator.
+ *
+ * Copyright (c) 2019, Heinrich Schuchardt <xypron.glpk@gmx.de>
+ */
+#include <common.h>
+#include <command.h>
+#include <dm.h>
+#include <hexdump.h>
+#include <rng.h>
+
+static int do_rng(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	size_t n = 0x40;
+	struct udevice *dev;
+	void *buf;
+	int ret = CMD_RET_SUCCESS;
+
+	if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
+		printf("No RNG device\n");
+		return CMD_RET_FAILURE;
+	}
+
+	if (argc >= 2)
+		n = simple_strtoul(argv[1], NULL, 16);
+
+	buf = malloc(n);
+	if (!buf) {
+		printf("Out of memory\n");
+		return CMD_RET_FAILURE;
+	}
+
+	if (dm_rng_read(dev, buf, n)) {
+		printf("Reading RNG failed\n");
+		ret = CMD_RET_FAILURE;
+	} else {
+		print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, buf, n);
+	}
+
+	free(buf);
+
+	return ret;
+}
+
+#ifdef CONFIG_SYS_LONGHELP
+static char rng_help_text[] =
+	"[n]\n"
+	"  - print n random bytes\n";
+#endif
+
+U_BOOT_CMD(
+	rng, 2, 0, do_rng,
+	"print bytes from the hardware random number generator",
+	rng_help_text
+);