| Message ID | 20240904234803.698424-4-masahiroy@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | kbuild: refactor DTB build rules, introduce a generic built-in boot DTB support | expand |
On Thu, Sep 05, 2024 at 08:47:39AM +0900, Masahiro Yamada wrote: > Some architectures support embedding boot DTB(s) in vmlinux. These > architectures, except MIPS and MicroBlaze, expect a single DTB in > the .dtb.init.rodata section. MIPS embeds multiple DTBs in vmlinux. > MicroBlaze embeds a DTB in its own __fdt_blob section instead of the > .dtb.init.rodata section. > > For example, RISC-V previously allowed embedding multiple DTBs, but > only the first DTB in the .dtb.init.rodata section was used. Commit > 2672031b20f6 ("riscv: dts: Move BUILTIN_DTB_SOURCE to common Kconfig") > ensured only one boot DTB is embedded. > > Meanwhile, commit 7b937cc243e5 ("of: Create of_root if no dtb provided > by firmware") introduced another DTB into the .dtb.init.rodata section. > > The symbol dump (sorted by address) for ARCH=riscv nommu_k210_defconfig > is now as follows: > > 00000000801290e0 D __dtb_start > 00000000801290e0 D __dtb_k210_generic_begin > 000000008012b571 D __dtb_k210_generic_end > 000000008012b580 D __dtb_empty_root_begin > 000000008012b5c8 D __dtb_empty_root_end > 000000008012b5e0 D __dtb_end > > The .dtb.init.rodata section contains the following two DTB files: > > arch/riscv/boot/dts/canaan/k210_generic.dtb > drivers/of/empty_root.dtb > > This is not an immediate problem because the boot code chooses the > first DTB, k210_generic.dtb. The second one, empty_root.dtb is ignored. > However, relying on the link order (i.e., the order in Makefiles) is > fragile. > > Only the boot DTB should be placed in the .dtb.init.rodata because the > arch boot code generally does not know the DT name, thus it uses the > __dtb_start symbol to find it. > > empty_root.dtb is looked up by name, so it can be moved to the generic > .init.rodata section. > > When CONFIG_OF_UNITTEST is enabled, more unittest DTBOs are embedded in > the .dtb.init.rodata section. These are also looked up by name, so can > be moved to the .init.rodata section. > > I added the __initdata annotation to the overlay_info data array because > modpost knows the .init.rodata section is discarded, and would otherwise > warn about it. > > The implementation is kind of cheesy; the section is .dtb.init.rodata > under the arch/ directory, and .init.rodata section otherwise. This will > be refactored later. > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> > --- > > drivers/of/unittest.c | 2 +- > scripts/Makefile.dtbs | 4 +++- > 2 files changed, 4 insertions(+), 2 deletions(-) Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c index fd8cb931b1cc..f5d18ae01c90 100644 --- a/drivers/of/unittest.c +++ b/drivers/of/unittest.c @@ -3585,7 +3585,7 @@ OVERLAY_INFO_EXTERN(overlay_bad_symbol); OVERLAY_INFO_EXTERN(overlay_bad_unresolved); /* entries found by name */ -static struct overlay_info overlays[] = { +static __initdata struct overlay_info overlays[] = { OVERLAY_INFO(overlay_base, -9999, 0), OVERLAY_INFO(overlay, 0, 0), OVERLAY_INFO(overlay_0, 0, 0), diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs index 46009d5f1486..55998b878e54 100644 --- a/scripts/Makefile.dtbs +++ b/scripts/Makefile.dtbs @@ -34,12 +34,14 @@ $(obj)/dtbs-list: $(dtb-y) FORCE # Assembly file to wrap dtb(o) # --------------------------------------------------------------------------- +builtin-dtb-section = $(if $(filter arch/%, $(obj)),.dtb.init.rodata,.init.rodata) + # Generate an assembly file to wrap the output of the device tree compiler quiet_cmd_wrap_S_dtb = WRAP $@ cmd_wrap_S_dtb = { \ symbase=__$(patsubst .%,%,$(suffix $<))_$(subst -,_,$(notdir $*)); \ echo '\#include <asm-generic/vmlinux.lds.h>'; \ - echo '.section .dtb.init.rodata,"a"'; \ + echo '.section $(builtin-dtb-section),"a"'; \ echo '.balign STRUCT_ALIGNMENT'; \ echo ".global $${symbase}_begin"; \ echo "$${symbase}_begin:"; \
Some architectures support embedding boot DTB(s) in vmlinux. These architectures, except MIPS and MicroBlaze, expect a single DTB in the .dtb.init.rodata section. MIPS embeds multiple DTBs in vmlinux. MicroBlaze embeds a DTB in its own __fdt_blob section instead of the .dtb.init.rodata section. For example, RISC-V previously allowed embedding multiple DTBs, but only the first DTB in the .dtb.init.rodata section was used. Commit 2672031b20f6 ("riscv: dts: Move BUILTIN_DTB_SOURCE to common Kconfig") ensured only one boot DTB is embedded. Meanwhile, commit 7b937cc243e5 ("of: Create of_root if no dtb provided by firmware") introduced another DTB into the .dtb.init.rodata section. The symbol dump (sorted by address) for ARCH=riscv nommu_k210_defconfig is now as follows: 00000000801290e0 D __dtb_start 00000000801290e0 D __dtb_k210_generic_begin 000000008012b571 D __dtb_k210_generic_end 000000008012b580 D __dtb_empty_root_begin 000000008012b5c8 D __dtb_empty_root_end 000000008012b5e0 D __dtb_end The .dtb.init.rodata section contains the following two DTB files: arch/riscv/boot/dts/canaan/k210_generic.dtb drivers/of/empty_root.dtb This is not an immediate problem because the boot code chooses the first DTB, k210_generic.dtb. The second one, empty_root.dtb is ignored. However, relying on the link order (i.e., the order in Makefiles) is fragile. Only the boot DTB should be placed in the .dtb.init.rodata because the arch boot code generally does not know the DT name, thus it uses the __dtb_start symbol to find it. empty_root.dtb is looked up by name, so it can be moved to the generic .init.rodata section. When CONFIG_OF_UNITTEST is enabled, more unittest DTBOs are embedded in the .dtb.init.rodata section. These are also looked up by name, so can be moved to the .init.rodata section. I added the __initdata annotation to the overlay_info data array because modpost knows the .init.rodata section is discarded, and would otherwise warn about it. The implementation is kind of cheesy; the section is .dtb.init.rodata under the arch/ directory, and .init.rodata section otherwise. This will be refactored later. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> --- drivers/of/unittest.c | 2 +- scripts/Makefile.dtbs | 4 +++- 2 files changed, 4 insertions(+), 2 deletions(-)