[PATCH] riscv: add BUILTIN_DTB support for MMU-enabled targets

[Vitaly Wool]

Sometimes, especially in a production system we may not want to
use a "smart bootloader" like u-boot to load kernel, ramdisk and
device tree from a filesystem on eMMC, but rather load the kernel
from a NAND partition and just run it as soon as we can, and in
this case it is convenient to have device tree compiled into the
kernel binary. Since this case is not limited to MMU-less systems,
let's support it for these which have MMU enabled too.

Signed-off-by: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
---
 arch/riscv/Kconfig   |  1 -
 arch/riscv/mm/init.c | 12 ++++++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 2b41f6d8e458..9464b4e3a71a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -419,7 +419,6 @@ endmenu
 
 config BUILTIN_DTB
 	def_bool n
-	depends on RISCV_M_MODE
 	depends on OF
 
 menu "Power management options"
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 87c305c566ac..5d1c7a3ec01c 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -194,12 +194,20 @@ void __init setup_bootmem(void)
 	setup_initrd();
 #endif /* CONFIG_BLK_DEV_INITRD */
 
+	/*
+	 * If DTB is built in, no need to reserve its memblock.
+	 * OTOH, initial_boot_params has to be set to properly copy DTB
+	 * before unflattening later on.
+	 */
+	if (IS_ENABLED(CONFIG_BUILTIN_DTB))
+		initial_boot_params = __va(dtb_early_pa);
+	else
+		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
+
 	/*
 	 * Avoid using early_init_fdt_reserve_self() since __pa() does
 	 * not work for DTB pointers that are fixmap addresses
 	 */
-	memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
-
 	early_init_fdt_scan_reserved_mem();
 	dma_contiguous_reserve(dma32_phys_limit);
 	memblock_allow_resize();
-- 
2.29.2