uboot-rockchip: increase rng-seed size

Increase rng-seed size to make Linux happy and initialize rng pool instantly.
Linux 5.19+ requires 32 bytes of entropy to initialize random pool, but u-boot
currently provides only 8 bytes.

Boot with 8 byte rng-seed (Linux 6.11):
    # dmesg | grep crng
    [   12.089286] random: crng init done
Boot with 32 byte rng-seed (Linux 6.11):
    # dmesg | grep crng
    [    0.000000] random: crng init done

Signed-off-by: Tianling Shen <[email protected]>
Link: openwrt/openwrt#17352
Signed-off-by: Hauke Mehrtens <[email protected]>

package/boot/uboot-rockchip/patches/001-rockchip-board-Increase-rng-seed-size-to-make-it-sufficie.patch

@@ -0,0 +1,96 @@
+From ed4ae7386257aa66455e330234e513d098a36f84 Mon Sep 17 00:00:00 2001
+From: Alex Shumsky <[email protected]>
+Date: Wed, 16 Oct 2024 13:02:03 +0300
+Subject: [PATCH] rockchip: board: Increase rng-seed size to make it sufficient
+ for modern Linux
+
+Increase rng-seed size to make Linux happy and initialize rng pool instantly.
+Linux 5.19+ requires 32 bytes of entropy to initialize random pool, but u-boot
+currently provides only 8 bytes.
+Linux 5.18 and probably some versions before it used to require 64 bytes.
+Bump min value to 64 bytes to be on a safe side.
+
+Boot with 8 byte rng-seed (Linux 6.11):
+    # dmesg | grep crng
+    [   12.089286] random: crng init done
+Boot with 32 byte rng-seed (Linux 6.11):
+    # dmesg | grep crng
+    [    0.000000] random: crng init done
+
+Linux source references:
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.19#n551
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.18#n236
+
+Signed-off-by: Alex Shumsky <[email protected]>
+Fixes: d2048bafae40 ("rockchip: board: Add board_rng_seed() for all Rockchip devices")
+Reviewed-by: Dragan Simic <[email protected]>
+Reviewed-by: Marek Vasut <[email protected]>
+Reviewed-by: Quentin Schulz <[email protected]>
+Reviewed-by: Kever Yang <[email protected]>
+---
+ arch/arm/mach-rockchip/board.c | 11 ++++++++++-
+ common/Kconfig                 |  3 +++
+ doc/usage/environment.rst      |  5 +++++
+ include/fdt_support.h          |  3 ++-
+ 4 files changed, 20 insertions(+), 2 deletions(-)
+
+--- a/arch/arm/mach-rockchip/board.c
++++ b/arch/arm/mach-rockchip/board.c
+@@ -480,9 +480,18 @@ __weak int misc_init_r(void)
+ __weak int board_rng_seed(struct abuf *buf)
+ {
+ 	struct udevice *dev;
+-	size_t len = 0x8;
++	ulong len = env_get_ulong("rng_seed_size", 10, 64);
+ 	u64 *data;
+
++	if (len < 64) {
++		/*
++		 * rng_seed_size should be at least 32 bytes for Linux 5.19+,
++		 * or 64 for older Linux kernel versions
++		 */
++		log_warning("Value for rng_seed_size (%lu) too low, Linux kernel RNG may fail to initialize early\n",
++			    len);
++	}
++
+ 	data = malloc(len);
+ 	if (!data) {
+ 		printf("Out of memory\n");
+--- a/common/Kconfig
++++ b/common/Kconfig
+@@ -927,6 +927,9 @@ config BOARD_RNG_SEED
+ 	  new seed for use on subsequent boots, and whether or not the
+ 	  kernel should account any entropy from the given seed.
+
++	  Default seed size (64 bytes) can be overridden by a decimal
++	  environment variable rng_seed_size.
++
+ endmenu
+
+ menu "Update support"
+--- a/doc/usage/environment.rst
++++ b/doc/usage/environment.rst
+@@ -323,6 +323,11 @@ netretry
+     Useful on scripts which control the retry operation
+     themselves.
+
++rng_seed_size
++    Size of random value added to device-tree node /chosen/rng-seed.
++    This variable is given as a decimal number.
++    If unset, 64 bytes is used as the default.
++
+ silent_linux
+     If set then Linux will be told to boot silently, by
+     adding 'console=' to its command line. If "yes" it will be
+--- a/include/fdt_support.h
++++ b/include/fdt_support.h
+@@ -202,7 +202,8 @@ int ft_board_setup(void *blob, struct bd
+  *
+  * This function is called if CONFIG_BOARD_RNG_SEED is set, and must
+  * be provided by the board. It should return, via @buf, some suitable
+- * seed value to pass to the kernel.
++ * seed value to pass to the kernel. Seed size could be set in a decimal
++ * environment variable rng_seed_size and it defaults to 64 bytes.
+  *
+  * @param buf         A struct abuf for returning the seed and its size.
+  * @return            0 if ok, negative on error.