[PATCH v2] 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>
---
Changelog from v1:
* no direct initial_boot_params assignment
* skips the temporary mapping for DT if BUILTIN_DTB=y 

 arch/riscv/Kconfig   |  1 -
 arch/riscv/mm/init.c | 15 +++++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 81b76d44725d..07a8bdcc423f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -416,7 +416,6 @@ 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 13ba533f462b..04aeee276817 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -191,10 +191,13 @@ void __init setup_bootmem(void)
 #endif /* CONFIG_BLK_DEV_INITRD */
 
 	/*
-	 * Avoid using early_init_fdt_reserve_self() since __pa() does
+	 * If DTB is built in, no need to reserve its memblock.
+	 * Otherwise, do reserve it but 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));
+	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
+		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
 
 	early_init_fdt_scan_reserved_mem();
 	dma_contiguous_reserve(dma32_phys_limit);
@@ -499,6 +502,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	/* Setup early PMD for DTB */
 	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
 			   (uintptr_t)early_dtb_pmd, PGDIR_SIZE, PAGE_TABLE);
+#ifndef CONFIG_BUILTIN_DTB
 	/* Create two consecutive PMD mappings for FDT early scan */
 	pa = dtb_pa & ~(PMD_SIZE - 1);
 	create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA,
@@ -506,7 +510,11 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA + PMD_SIZE,
 			   pa + PMD_SIZE, PMD_SIZE, PAGE_KERNEL);
 	dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PMD_SIZE - 1));
+#else /* CONFIG_BUILTIN_DTB */
+	dtb_early_va = __va(dtb_pa);
+#endif /* CONFIG_BUILTIN_DTB */
 #else
+#ifndef CONFIG_BUILTIN_DTB
 	/* Create two consecutive PGD mappings for FDT early scan */
 	pa = dtb_pa & ~(PGDIR_SIZE - 1);
 	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
@@ -514,6 +522,9 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA + PGDIR_SIZE,
 			   pa + PGDIR_SIZE, PGDIR_SIZE, PAGE_KERNEL);
 	dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PGDIR_SIZE - 1));
+#else /* CONFIG_BUILTIN_DTB */
+	dtb_early_va = __va(dtb_pa);
+#endif /* CONFIG_BUILTIN_DTB */
 #endif
 	dtb_early_pa = dtb_pa;
 
-- 
2.20.1