LoongArch: Allow device trees be built into the kernel

During the upstream progress of those DT-based drivers, DT properties
are changed a lot so very different from those in existing bootloaders.
It is inevitably that some existing systems do not provide a standard,
canonical device tree to the kernel at boot time. So let's provide a
device tree table in the kernel, keyed by the dts filename, containing
the relevant DTBs.

We can use the built-in dts files as references. Each SoC has only one
built-in dts file which describes all possible device information of
that SoC, so the dts files are good examples during development.

And as a reference, our built-in dts file only enables the most basic
bootable combinations (so it is generic enough), acts as an alternative
in case the dts in the bootloader is unexpected.

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kbuild

@@ -4,6 +4,7 @@ obj-y += net/
 obj-y += vdso/
 
 obj-$(CONFIG_KVM) += kvm/
+obj-$(CONFIG_BUILTIN_DTB) += boot/dts/
 
 # for cleaning
 subdir- += boot

arch/loongarch/Kconfig

@@ -375,6 +375,24 @@ config CMDLINE_FORCE
 
 endchoice
 
+config BUILTIN_DTB
+	bool "Enable built-in dtb in kernel"
+	depends on OF
+	help
+	  Some existing systems do not provide a canonical device tree to
+	  the kernel at boot time. Let's provide a device tree table in the
+	  kernel, keyed by the dts filename, containing the relevant DTBs.
+
+	  Built-in DTBs are generic enough and can be used as references.
+
+config BUILTIN_DTB_NAME
+	string "Source file for built-in dtb"
+	depends on BUILTIN_DTB
+	help
+	  Base name (without suffix, relative to arch/loongarch/boot/dts/)
+	  for the DTS file that will be used to produce the DTB linked into
+	  the kernel.
+
 config DMI
 	bool "Enable DMI scanning"
 	select DMI_SCAN_MACHINE_NON_EFI_FALLBACK

arch/loongarch/Makefile

@@ -6,6 +6,7 @@
 boot	:= arch/loongarch/boot
 
 KBUILD_DEFCONFIG := loongson3_defconfig
+KBUILD_DTBS      := dtbs
 
 image-name-y			:= vmlinux
 image-name-$(CONFIG_EFI_ZBOOT)	:= vmlinuz
@@ -144,7 +145,7 @@ endif
 
 vdso-install-y += arch/loongarch/vdso/vdso.so.dbg
 
-all:	$(notdir $(KBUILD_IMAGE))
+all:	$(notdir $(KBUILD_IMAGE)) $(KBUILD_DTBS)
 
 vmlinuz.efi: vmlinux.efi
 

arch/loongarch/boot/dts/Makefile

@@ -1,4 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
-dtstree	:= $(srctree)/$(src)
 
-dtb-y := $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dtstree)/*.dts))
+obj-$(CONFIG_BUILTIN_DTB)	+= $(addsuffix .dtb.o, $(CONFIG_BUILTIN_DTB_NAME))

arch/loongarch/kernel/setup.c

@@ -295,8 +295,12 @@ static void __init fdt_setup(void)
 	if (acpi_os_get_root_pointer())
 		return;
 
-	/* Look for a device tree configuration table entry */
+	/* Prefer to use built-in dtb, checking its legality first. */
-	fdt_pointer = efi_fdt_pointer();
+	if (!fdt_check_header(__dtb_start))
+		fdt_pointer = __dtb_start;
+	else
+		fdt_pointer = efi_fdt_pointer(); /* Fallback to firmware dtb */
+
 	if (!fdt_pointer || fdt_check_header(fdt_pointer))
 		return;
 
@@ -330,7 +334,9 @@ static void __init bootcmdline_init(char **cmdline_p)
 		if (boot_command_line[0])
 			strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
 
-		strlcat(boot_command_line, init_command_line, COMMAND_LINE_SIZE);
+		if (!strstr(boot_command_line, init_command_line))
+			strlcat(boot_command_line, init_command_line, COMMAND_LINE_SIZE);
+
 		goto out;
 	}
 #endif