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From 318c1fce4aeef298cbb6153416c499c94ad7cda0 Mon Sep 17 00:00:00 2001
From: Jonas Gorski <jogo@openwrt.org>
Date: Tue, 24 Jun 2014 10:53:15 +0200
Subject: [PATCH RFC v3] MIPS: add support for vmlinux.bin appended DTB
Add support for populating initial_boot_params through a dtb
blob appended to raw vmlinux.bin.
Signed-off-by: Jonas Gorski <jogo@openwrt.org>
---
Changes RFC v2 -> v3
* fixed !smp kernels (TODO: move it to its own patch
Changes RFC v1 -> v2
* changed all occurences of vmlinux to vmlinux.bin
* clarified this applies to the raw vmlinux.bin without decompressor
* s/initial_device_params/initial_boot_params/
Initial comments by me still valid:
Mostly adapted from how ARM is doing it.
Sent as an RFC PATCH because I am not sure if this is the right way to
it, and whether storing the pointer in initial_boot_params is a good
idea, or a new variable should be introduced.
The reasoning for initial_boot_params is that there is no common
MIPS interface yet, so the next best thing was using that. This also
has the advantage of keeping the original fw_args intact.
This patch works for me on bcm63xx, where the bootloader expects
an lzma compressed kernel, so I didn't want to double compress using
the in-kernel compressed kernel support.
Completely untested on anything except MIPS32 / big endian.
arch/mips/Kconfig | 18 ++++++++++++++++++
arch/mips/kernel/head.S | 19 +++++++++++++++++++
arch/mips/kernel/vmlinux.lds.S | 7 +++++++
3 files changed, 43 insertions(+)
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2519,6 +2519,24 @@ config RAPIDIO
source "drivers/rapidio/Kconfig"
+config MIPS_APPENDED_DTB
+ bool "Use appended device tree blob to vmlinux.bin (EXPERIMENTAL)"
+ depends on OF
+ help
+ With this option, the boot code will look for a device tree binary
+ DTB) appended to raw vmlinux.bin (without decompressor).
+ (e.g. cat vmlinux.bin <filename>.dtb > vmlinux_w_dtb).
+
+ This is meant as a backward compatibility convenience for those
+ systems with a bootloader that can't be upgraded to accommodate
+ the documented boot protocol using a device tree.
+
+ Beware that there is very little in terms of protection against
+ this option being confused by leftover garbage in memory that might
+ look like a DTB header after a reboot if no actual DTB is appended
+ to vmlinux.bin. Do not leave this option active in a production kernel
+ if you don't intend to always append a DTB.
+
endmenu
menu "Executable file formats"
--- a/arch/mips/kernel/head.S
+++ b/arch/mips/kernel/head.S
@@ -139,6 +139,22 @@ NESTED(kernel_entry, 16, sp) # kernel
mtc0 t0, CP0_STATUS
#endif /* CONFIG_MIPS_MT_SMTC */
+#ifdef CONFIG_MIPS_APPENDED_DTB
+ PTR_LA t0, __appended_dtb
+ PTR_LI t3, 0
+
+#ifdef CONFIG_CPU_BIG_ENDIAN
+ PTR_LI t1, 0xd00dfeed
+#else
+ PTR_LI t1, 0xedfe0dd0
+#endif
+ LONG_L t2, (t0)
+ bne t1, t2, not_found
+
+ PTR_LA t3, __appended_dtb
+
+not_found:
+#endif
PTR_LA t0, __bss_start # clear .bss
LONG_S zero, (t0)
PTR_LA t1, __bss_stop - LONGSIZE
@@ -152,6 +168,10 @@ NESTED(kernel_entry, 16, sp) # kernel
LONG_S a2, fw_arg2
LONG_S a3, fw_arg3
+#ifdef CONFIG_MIPS_APPENDED_DTB
+ LONG_S t3, initial_boot_params
+#endif
+
MTC0 zero, CP0_CONTEXT # clear context register
PTR_LA $28, init_thread_union
/* Set the SP after an empty pt_regs. */
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -125,8 +125,14 @@ SECTIONS
.exit.data : {
EXIT_DATA
}
-
+#ifdef CONFIG_SMP
PERCPU_SECTION(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
+#endif
+#ifdef CONFIG_MIPS_APPENDED_DTB
+ __appended_dtb = .;
+ /* leave space for appended DTB */
+ . = . + 0x100000;
+#endif
/*
* Align to 64K in attempt to eliminate holes before the
* .bss..swapper_pg_dir section at the start of .bss. This
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