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From 318c1fce4aeef298cbb6153416c499c94ad7cda0 Mon Sep 17 00:00:00 2001
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From: Jonas Gorski <jogo@openwrt.org>
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Date: Tue, 24 Jun 2014 10:53:15 +0200
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Subject: [PATCH RFC v3] MIPS: add support for vmlinux.bin appended DTB
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Add support for populating initial_boot_params through a dtb
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blob appended to raw vmlinux.bin.
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Signed-off-by: Jonas Gorski <jogo@openwrt.org>
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---
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Changes RFC v2 -> v3
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* fixed !smp kernels (TODO: move it to its own patch
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Changes RFC v1 -> v2
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* changed all occurences of vmlinux to vmlinux.bin
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* clarified this applies to the raw vmlinux.bin without decompressor
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* s/initial_device_params/initial_boot_params/
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Initial comments by me still valid:
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Mostly adapted from how ARM is doing it.
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Sent as an RFC PATCH because I am not sure if this is the right way to
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it, and whether storing the pointer in initial_boot_params is a good
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idea, or a new variable should be introduced.
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The reasoning for initial_boot_params is that there is no common
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MIPS interface yet, so the next best thing was using that. This also
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has the advantage of keeping the original fw_args intact.
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This patch works for me on bcm63xx, where the bootloader expects
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an lzma compressed kernel, so I didn't want to double compress using
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the in-kernel compressed kernel support.
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Completely untested on anything except MIPS32 / big endian.
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arch/mips/Kconfig | 18 ++++++++++++++++++
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arch/mips/kernel/head.S | 19 +++++++++++++++++++
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arch/mips/kernel/vmlinux.lds.S | 7 +++++++
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3 files changed, 43 insertions(+)
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--- a/arch/mips/Kconfig
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+++ b/arch/mips/Kconfig
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@@ -2655,6 +2655,24 @@ config RAPIDIO
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source "drivers/rapidio/Kconfig"
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+config MIPS_APPENDED_DTB
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+ bool "Use appended device tree blob to vmlinux.bin (EXPERIMENTAL)"
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+ depends on OF
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+ help
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+ With this option, the boot code will look for a device tree binary
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+ DTB) appended to raw vmlinux.bin (without decompressor).
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+ (e.g. cat vmlinux.bin <filename>.dtb > vmlinux_w_dtb).
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+
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+ This is meant as a backward compatibility convenience for those
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+ systems with a bootloader that can't be upgraded to accommodate
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+ the documented boot protocol using a device tree.
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+
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+ Beware that there is very little in terms of protection against
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+ this option being confused by leftover garbage in memory that might
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+ look like a DTB header after a reboot if no actual DTB is appended
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+ to vmlinux.bin. Do not leave this option active in a production kernel
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+ if you don't intend to always append a DTB.
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+
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endmenu
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menu "Executable file formats"
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--- a/arch/mips/kernel/head.S
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+++ b/arch/mips/kernel/head.S
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@@ -100,6 +100,22 @@ NESTED(kernel_entry, 16, sp) # kernel
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jr t0
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0:
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+#ifdef CONFIG_MIPS_APPENDED_DTB
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+ PTR_LA t0, __appended_dtb
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+ PTR_LI t3, 0
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+
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+#ifdef CONFIG_CPU_BIG_ENDIAN
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+ PTR_LI t1, 0xd00dfeed
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+#else
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+ PTR_LI t1, 0xedfe0dd0
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+#endif
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+ LONG_L t2, (t0)
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+ bne t1, t2, not_found
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+
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+ PTR_LA t3, __appended_dtb
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+
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+not_found:
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+#endif
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PTR_LA t0, __bss_start # clear .bss
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LONG_S zero, (t0)
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PTR_LA t1, __bss_stop - LONGSIZE
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@@ -113,6 +129,10 @@ NESTED(kernel_entry, 16, sp) # kernel
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LONG_S a2, fw_arg2
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LONG_S a3, fw_arg3
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+#ifdef CONFIG_MIPS_APPENDED_DTB
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+ LONG_S t3, initial_boot_params
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+#endif
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+
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MTC0 zero, CP0_CONTEXT # clear context register
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PTR_LA $28, init_thread_union
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/* Set the SP after an empty pt_regs. */
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--- a/arch/mips/kernel/vmlinux.lds.S
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+++ b/arch/mips/kernel/vmlinux.lds.S
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@@ -125,8 +125,14 @@ SECTIONS
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.exit.data : {
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EXIT_DATA
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}
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-
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+#ifdef CONFIG_SMP
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PERCPU_SECTION(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
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+#endif
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+#ifdef CONFIG_MIPS_APPENDED_DTB
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+ __appended_dtb = .;
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+ /* leave space for appended DTB */
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+ . = . + 0x100000;
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+#endif
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/*
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* Align to 64K in attempt to eliminate holes before the
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* .bss..swapper_pg_dir section at the start of .bss. This
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