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From: Alexey Brodkin <abrodkin@synopsys.com>
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Subject: openwrt: arc - add OWRTDTB section
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This change allows OpenWRT to patch resulting kernel binary with
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external .dtb.
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That allows us to re-use exactky the same vmlinux on different boards
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given its ARC core configurations match (at least cache line sizes etc).
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""patch-dtb" searches for ASCII "OWRTDTB:" strign and copies external
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.dtb right after it, keeping the string in place.
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Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
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---
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arch/arc/kernel/head.S | 10 ++++++++++
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arch/arc/kernel/setup.c | 4 +++-
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arch/arc/kernel/vmlinux.lds.S | 13 +++++++++++++
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3 files changed, 26 insertions(+), 1 deletion(-)
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--- a/arch/arc/kernel/head.S
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+++ b/arch/arc/kernel/head.S
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@@ -49,6 +49,16 @@
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1:
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.endm
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+; Here "patch-dtb" will embed external .dtb
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+; Note "patch-dtb" searches for ASCII "OWRTDTB:" string
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+; and pastes .dtb right after it, hense the string precedes
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+; __image_dtb symbol.
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+ .section .owrt, "aw",@progbits
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+ .ascii "OWRTDTB:"
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+ENTRY(__image_dtb)
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+ .fill 0x4000
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+END(__image_dtb)
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+
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.section .init.text, "ax",@progbits
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;----------------------------------------------------------------
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--- a/arch/arc/kernel/setup.c
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+++ b/arch/arc/kernel/setup.c
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@@ -456,6 +456,8 @@ static inline int is_kernel(unsigned lon
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return 0;
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}
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+extern struct boot_param_header __image_dtb;
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+
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void __init setup_arch(char **cmdline_p)
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{
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#ifdef CONFIG_ARC_UBOOT_SUPPORT
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@@ -469,7 +471,7 @@ void __init setup_arch(char **cmdline_p)
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#endif
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{
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/* No, so try the embedded one */
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- machine_desc = setup_machine_fdt(__dtb_start);
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+ machine_desc = setup_machine_fdt(&__image_dtb);
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if (!machine_desc)
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panic("Embedded DT invalid\n");
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--- a/arch/arc/kernel/vmlinux.lds.S
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+++ b/arch/arc/kernel/vmlinux.lds.S
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@@ -30,6 +30,19 @@ SECTIONS
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. = CONFIG_LINUX_LINK_BASE;
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+ /*
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+ * In OpenWRT we want to patch built binary embedding .dtb of choice.
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+ * This is implemented with "patch-dtb" utility which searches for
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+ * "OWRTDTB:" string in first 16k of image and if it is found
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+ * copies .dtb right after mentioned string.
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+ *
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+ * Note: "OWRTDTB:" won't be overwritten with .dtb, .dtb will follow it.
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+ */
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+ .owrt : {
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+ *(.owrt)
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+ . = ALIGN(PAGE_SIZE);
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+ }
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+
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_int_vec_base_lds = .;
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.vector : {
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*(.vector)
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