[PATCH RFC v2] MIPS: add support for vmlinux.bin appended DTB

[PATCH RFC v2] MIPS: add support for vmlinux.bin appended DTB

[Jonas Gorski]

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 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 |  6 ++++++
 3 files changed, 43 insertions(+)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 3f05b56..21c6d51 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2476,6 +2476,24 @@ config USE_OF
 	select OF_EARLY_FLATTREE
 	select IRQ_DOMAIN
 
+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
 
 config LOCKDEP_SUPPORT
diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S
index 95afd66..72c1049 100644
--- a/arch/mips/kernel/head.S
+++ b/arch/mips/kernel/head.S
@@ -93,7 +93,22 @@ NESTED(kernel_entry, 16, sp)			# kernel entry point
 	PTR_LA	t0, 0f
 	jr	t0
 0:
+#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
@@ -107,6 +122,10 @@ NESTED(kernel_entry, 16, sp)			# kernel entry point
 	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.  */
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index 3b46f7c..8009530 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -127,6 +127,12 @@ SECTIONS
 	}
 
 	PERCPU_SECTION(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
+
+#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
-- 
2.0.0

Re: [PATCH RFC v2] MIPS: add support for vmlinux.bin appended DTB

[Jonas Gorski]

On Sat, Jul 12, 2014 at 12:49 PM, Jonas Gorski <jogo@openwrt.org> wrote:
> (snip)
> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> index 3b46f7c..8009530 100644
> --- a/arch/mips/kernel/vmlinux.lds.S
> +++ b/arch/mips/kernel/vmlinux.lds.S
> @@ -127,6 +127,12 @@ SECTIONS
>         }
>
>         PERCPU_SECTION(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
> +
> +#ifdef CONFIG_MIPS_APPENDED_DTB
> +       __appended_dtb = .;
> +       /* leave space for appended DTB */
> +       . = . + 0x100000;
> +#endif

Okay, this won't work for non SMP kernels - PERCPU is empty there, so
the actual binary end is then __mips_machine_end, not __per_cpu_end
(unless mips_machine_end happens to satisfty the per_cpu alignment
requirements).

So back to the drawing board.


Jonas

Re: [PATCH RFC v2] MIPS: add support for vmlinux.bin appended DTB

[Aaro Koskinen]

Hi,

On Fri, Aug 08, 2014 at 08:39:48PM +0200, Jonas Gorski wrote:
> On Sat, Jul 12, 2014 at 12:49 PM, Jonas Gorski <jogo@openwrt.org> wrote:
> > (snip)
> > diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> > index 3b46f7c..8009530 100644
> > --- a/arch/mips/kernel/vmlinux.lds.S
> > +++ b/arch/mips/kernel/vmlinux.lds.S
> > @@ -127,6 +127,12 @@ SECTIONS
> >         }
> >
> >         PERCPU_SECTION(1 << CONFIG_MIPS_L1_CACHE_SHIFT)
> > +
> > +#ifdef CONFIG_MIPS_APPENDED_DTB
> > +       __appended_dtb = .;
> > +       /* leave space for appended DTB */
> > +       . = . + 0x100000;
> > +#endif
> 
> Okay, this won't work for non SMP kernels - PERCPU is empty there, so
> the actual binary end is then __mips_machine_end, not __per_cpu_end
> (unless mips_machine_end happens to satisfty the per_cpu alignment
> requirements).
> 
> So back to the drawing board.

Any news? Would it work just by not defining PERCPU on non-SMP builds?

A.