arm: init: save previous bootloader data

When u-boot is used as a chain-loaded bootloader (replacing OS kernel),
previous bootloader leaves data in RAM, that can be reused.

For example, on recent arm linux system, when chainloading u-boot,
there are initramfs and fdt in RAM prepared for OS booting. Initramfs
may be modified to store u-boot's payload, thus providing the ability to
use chainloaded u-boot to boot OS without any storage support.

Two config options added:
- SAVE_PREV_BL_INITRAMFS_START_ADDR
  saves initramfs start address to 'prevbl_initrd_start_addr' environment
  variable
- SAVE_PREV_BL_FDT_ADDR
  saves fdt address to 'prevbl_fdt_addr' environment variable

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
Cc: Tom Rini <trini@konsulko.com>

2 files changed, 96 insertions, 0 deletions

diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 594fc12..c603fe6 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -48,6 +48,11 @@ obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMCPY) += memcpy.o
 endif
 obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += semihosting.o
 
+ifneq ($(filter y,$(CONFIG_SAVE_PREV_BL_INITRAMFS_START_ADDR) $(CONFIG_SAVE_PREV_BL_FDT_ADDR)),)
+obj-y += save_prev_bl_data.o
+endif
+
+# obj-$(CONFIG_SAVE_PREV_BL_INITRAMFS_START_ADDR) += save_prev_bl_data.o
 obj-y	+= bdinfo.o
 obj-y	+= sections.o
 CFLAGS_REMOVE_sections.o := $(LTO_CFLAGS)
diff --git a/arch/arm/lib/save_prev_bl_data.c b/arch/arm/lib/save_prev_bl_data.c
new file mode 100644
index 0000000..f4ee86a
--- /dev/null
+++ b/arch/arm/lib/save_prev_bl_data.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * save_prev_bl_data - saving previous bootloader data
+ * to environment variables.
+ *
+ * Copyright (c) 2022 Dzmitry Sankouski (dsankouski@gmail.com)
+ */
+#include <init.h>
+#include <env.h>
+#include <fdtdec.h>
+#include <fdt_support.h>
+#include <fdt.h>
+#include <common.h>
+#include <linux/errno.h>
+#include <asm/system.h>
+#include <asm/armv8/mmu.h>
+
+static ulong reg0 __section(".data");
+
+/**
+ * Save x0 register value, assuming previous bootloader set it to
+ * point on loaded fdt or (for older linux kernels)atags.
+ */
+void save_boot_params(ulong r0)
+{
+	reg0 = r0;
+	save_boot_params_ret();
+}
+
+bool is_addr_accessible(phys_addr_t addr)
+{
+	struct mm_region *mem = mem_map;
+	phys_addr_t bank_start;
+	phys_addr_t bank_end;
+
+	while (mem->size) {
+		bank_start = mem->phys;
+		bank_end = bank_start + mem->size;
+		debug("check if block %pap - %pap includes %pap\n", &bank_start, &bank_end, &addr);
+		if (addr > bank_start && addr < bank_end)
+			return true;
+		mem++;
+	}
+
+	return false;
+}
+
+int save_prev_bl_data(void)
+{
+	struct fdt_header *fdt_blob;
+	int node;
+	u64 initrd_start_prop;
+
+	if (!is_addr_accessible((phys_addr_t)reg0))
+		return -ENODATA;
+
+	fdt_blob = (struct fdt_header *)reg0;
+	if (!fdt_valid(&fdt_blob)) {
+		pr_warn("%s: address 0x%lx is not a valid fdt\n", __func__, reg0);
+		return -ENODATA;
+	}
+
+	if (CONFIG_IS_ENABLED(SAVE_PREV_BL_FDT_ADDR))
+		env_set_addr("prevbl_fdt_addr", (void *)reg0);
+	if (!CONFIG_IS_ENABLED(SAVE_PREV_BL_INITRAMFS_START_ADDR))
+		return 0;
+
+	node = fdt_path_offset(fdt_blob, "/chosen");
+	if (!node) {
+		pr_warn("%s: chosen node not found in device tree at addr: 0x%lx\n",
+					__func__, reg0);
+		return -ENODATA;
+	}
+	/*
+	 * linux,initrd-start property might be either 64 or 32 bit,
+	 * depending on primary bootloader implementation.
+	 */
+	initrd_start_prop = fdtdec_get_uint64(fdt_blob, node, "linux,initrd-start", 0);
+	if (!initrd_start_prop) {
+		debug("%s: attempt to get uint64 linux,initrd-start property failed, trying uint\n",
+				__func__);
+		initrd_start_prop = fdtdec_get_uint(fdt_blob, node, "linux,initrd-start", 0);
+		if (!initrd_start_prop) {
+			debug("%s: attempt to get uint failed, too\n", __func__);
+			return -ENODATA;
+		}
+	}
+	env_set_addr("prevbl_initrd_start_addr", (void *)initrd_start_prop);
+
+	return 0;
+}