riscv: add BUILTIN_DTB support for MMU-enabled targets

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.

While at it, provide __dtb_start as a parameter to setup_vm() in
BUILTIN_DTB case, so we don't have to duplicate BUILTIN_DTB specific
processing in MMU-enabled and MMU-disabled versions of setup_vm().
Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -460,7 +460,6 @@ endmenu
 
 config BUILTIN_DTB
 	def_bool n
-	depends on RISCV_M_MODE
 	depends on OF
 
 menu "Power management options"

arch/riscv/kernel/head.S

@@ -260,7 +260,11 @@ clear_bss_done:
 
 	/* Initialize page tables and relocate to virtual addresses */
 	la sp, init_thread_union + THREAD_SIZE
+#ifdef CONFIG_BUILTIN_DTB
+	la a0, __dtb_start
+#else
 	mv a0, s1
+#endif /* CONFIG_BUILTIN_DTB */
 	call setup_vm
 #ifdef CONFIG_MMU
 	la a0, early_pg_dir

arch/riscv/mm/init.c

@@ -192,9 +192,12 @@ 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
 	 */
+	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
 		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
 
 	early_init_fdt_scan_reserved_mem();
@@ -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;
 
@@ -604,11 +615,7 @@ static void __init setup_vm_final(void)
 #else
 asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
-#ifdef CONFIG_BUILTIN_DTB
-	dtb_early_va = (void *) __dtb_start;
-#else
 	dtb_early_va = (void *)dtb_pa;
-#endif
 	dtb_early_pa = dtb_pa;
 }