[v4,2/9] riscv: Add BUILTIN_DTB support

Commit Message

Damien Le Moal March 16, 2020, 12:47 a.m. UTC

For the NOMMU case, enable a kernel builtin dtb to allow direct kernel
loading without a bootloader. This option also allows booting on boards
not capable of providing a device tree to the bootloader.

Signed-off-by: Damien Le Moal <[e-mail]>
Reviewed-by: Atish Patra <[e-mail]>
---
 arch/riscv/Kbuild            |  1 +
 arch/riscv/Kconfig           | 19 +++++++++++++++++++
 arch/riscv/boot/dts/Makefile |  4 ++++
 arch/riscv/kernel/setup.c    |  6 ++++++
 arch/riscv/mm/init.c         |  4 ++++
 5 files changed, 34 insertions(+)

Patch

diff --git a/arch/riscv/Kbuild b/arch/riscv/Kbuild
index d1d0aa70fdf1..988804e430e4 100644
--- a/arch/riscv/Kbuild
+++ b/arch/riscv/Kbuild
@@ -1,3 +1,4 @@ 
 # SPDX-License-Identifier: GPL-2.0-only
 
 obj-y += kernel/ mm/ net/
+obj-$(CONFIG_USE_BUILTIN_DTB)	+= boot/dts/
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 1a3b5a5276be..025f5ba1dd68 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -355,6 +355,25 @@  config CMDLINE_FORCE
 
 endchoice
 
+config USE_BUILTIN_DTB
+	bool "Use builtin DTB"
+	depends on !MMU
+	help
+	  Link a device tree blob for particular hardware into the kernel,
+	  suppressing use of the DTB pointer provided by the bootloader.
+	  This option should only be used with hardware or bootloaders that
+	  are not capable of providing a DTB to the kernel, or for
+	  experimental hardware without stable device tree bindings.
+
+config BUILTIN_DTB_SOURCE
+	string "Source file for builtin DTB"
+	default ""
+	depends on USE_BUILTIN_DTB
+	help
+	  Base name (without suffix, relative to arch/riscv/boot/dts) for
+	  the a DTS file that will be used to produce the DTB linked into
+	  the kernel.
+
 endmenu
 
 menu "Power management options"
diff --git a/arch/riscv/boot/dts/Makefile b/arch/riscv/boot/dts/Makefile
index dcc3ada78455..0bf2669aa12d 100644
--- a/arch/riscv/boot/dts/Makefile
+++ b/arch/riscv/boot/dts/Makefile
@@ -1,2 +1,6 @@ 
 # SPDX-License-Identifier: GPL-2.0
+ifneq ($(CONFIG_BUILTIN_DTB_SOURCE),"")
+obj-$(CONFIG_USE_BUILTIN_DTB) += $(patsubst "%",%,$(CONFIG_BUILTIN_DTB_SOURCE)).dtb.o
+else
 subdir-y += sifive
+endif
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 0a6d415b0a5a..3e89be9d888c 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -68,7 +68,13 @@  void __init setup_arch(char **cmdline_p)
 
 	setup_bootmem();
 	paging_init();
+
+#if IS_ENABLED(CONFIG_USE_BUILTIN_DTB)
+	unflatten_and_copy_device_tree();
+#else
 	unflatten_device_tree();
+#endif
+
 	clint_init_boot_cpu();
 
 #ifdef CONFIG_SWIOTLB
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index fab855963c73..51f1ee0a24a6 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -480,7 +480,11 @@  static void __init setup_vm_final(void)
 #else
 asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
+#if IS_ENABLED(CONFIG_USE_BUILTIN_DTB)
+	dtb_early_va = __dtb_start;
+#else
 	dtb_early_va = (void *)dtb_pa;
+#endif
 }
 
 static inline void setup_vm_final(void)