>From 464df9cb918d46fcbe5552b46b2fe7f916fdd0b4 Mon Sep 17 00:00:00 2001 From: Daniel Gimpelevich <daniel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> Date: Mon, 23 May 2016 22:19:42 -0700 Subject: [RFC PATCH] Re: Adding support for device tree and command line On Mon, 2016-05-23 at 15:12 -0700, Daniel Gimpelevich wrote: > On Mon, 2016-05-23 at 23:34 +0200, Hauke Mehrtens wrote: > > On 05/23/2016 11:14 PM, Hauke Mehrtens wrote: > > > Section 3 of this document defines some interfaces how a boot loader > > > could forward a command line *or* a device tree to the kernel: > > > http://wiki.prplfoundation.org/w/images/4/42/UHI_Reference_Manual.pdf > > > This allows only a device tree *or* a command line, not both. > > > > > > The Linux kernel also supports an appended device tree. In this case the > > > early code overwrites the fw_args to look like the boot loader added a > > > device tree. This is done when CONFIG_MIPS_RAW_APPENDED_DTB is activated. > > > > > > The problem is when we use an appended device tree and the boot loader > > > adds some important information in the kernel command line. In this case > > > the command line gets overwritten and we do not get this information. > > > This is the case for some lantiq devices were the boot loader provides > > > the mac address to the kernel via the kernel command line. > > > > > > My proposal to solve this problem is to extend the interface and add a > > > option to provide the kernel command line *and* a device tree from the > > > boot loader to the kernel. > > > > > > a) use fw_arg0 ($a0) = -2 and fill the unused registers fw_arg2 ($a2) > > > and fw_arg3 ($a3) with argv and envp. > > > > > > b) add a new boot protocol $a0 = -3 with $a1 = DT address, $a2 = argv > > > and $a3 = envp. > > > > I just looked a little bit more closely and saw that the command line > > uses 3 args. One for the count, one argv and one envp. > > > > I would then only support device tree + count and argv, so the new > > interface would not support envp. > > > > > > > > I would prefer solution b). > > > > > > This way we would not loose the kernel command line when appending a > > > device tree and this could also be used by the boot loader if someone > > > wants to. > > > > > > Should I send a patch for this? > > > > > > Hauke > > It was because I looked through the above-linked UHI spec that I became > concerned about CONFIG_MIPS_RAW_APPENDED_DTB only mimicking, rather than > fully implementing, real UHI. In the upstream kernel, the new $a0 == -2 > code can be a starting point for adding UHI argv/envp parsing for when a > UHI-compliant bootloader is used. However, on the head.S side, what I > propose for the lantiq target is to remove CONFIG_MIPS_RAW_APPENDED_DTB > from the kernel config, and reintroduce this as a platform patch: > https://github.com/openwrt/openwrt/blob/b3158f781f24ac2ec1c0da86479bfc156c52c80b/target/linux/lantiq/patches-4.4/0036-owrt-generic-dtb-image-hack.patch > The brcm63xx target could then retain CONFIG_MIPS_RAW_APPENDED_DTB, or > not, depending on bootloader specifics there, which I have not > investigated, and likewise the various other targets to which > CONFIG_MIPS_RAW_APPENDED_DTB has since been extended even though it was > apparently initially only an expedient hack only for brcm63xx. > > Using $a0 = -3 is expressly prohibited in the above UHI document, and > using $a2/$a3 "would risk becoming incompatible with existing UHI > compliant implementations." I have come up with a more elegant solution: Simply move the register substitution from head.S to just before it matters. You can still override the boot args using CONFIG_MIPS_CMDLINE_FROM_DTB. Signed-off-by: Daniel Gimpelevich <daniel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> --- arch/mips/bmips/setup.c | 7 +++++++ arch/mips/boot/compressed/head.S | 16 ---------------- arch/mips/include/asm/prom.h | 5 +++++ arch/mips/kernel/head.S | 16 ---------------- arch/mips/lantiq/prom.c | 7 +++++++ 5 files changed, 19 insertions(+), 32 deletions(-) diff --git a/arch/mips/bmips/setup.c b/arch/mips/bmips/setup.c index f146d12..2711c36 100644 --- a/arch/mips/bmips/setup.c +++ b/arch/mips/bmips/setup.c @@ -160,6 +160,13 @@ void __init plat_mem_setup(void) ioport_resource.end = ~0; /* intended to somewhat resemble ARM; see Documentation/arm/Booting */ +#if defined(CONFIG_MIPS_RAW_APPENDED_DTB) ||\ + defined(CONFIG_MIPS_ZBOOT_APPENDED_DTB) + if (be32_to_cpup((__be32 *)__appended_dtb) == 0xd00dfeed) { + fw_arg0 = -2; + fw_arg1 = (unsigned long)__appended_dtb; + } +#endif if (fw_arg0 == 0 && fw_arg1 == 0xffffffff) dtb = phys_to_virt(fw_arg2); else if (fw_arg0 == -2) /* UHI interface */ diff --git a/arch/mips/boot/compressed/head.S b/arch/mips/boot/compressed/head.S index c580e85..409cb48 100644 --- a/arch/mips/boot/compressed/head.S +++ b/arch/mips/boot/compressed/head.S @@ -25,22 +25,6 @@ start: move s2, a2 move s3, a3 -#ifdef CONFIG_MIPS_ZBOOT_APPENDED_DTB - PTR_LA t0, __appended_dtb -#ifdef CONFIG_CPU_BIG_ENDIAN - li t1, 0xd00dfeed -#else - li t1, 0xedfe0dd0 -#endif - lw t2, (t0) - bne t1, t2, not_found - nop - - move s1, t0 - PTR_LI s0, -2 -not_found: -#endif - /* Clear BSS */ PTR_LA a0, _edata PTR_LA a2, _end diff --git a/arch/mips/include/asm/prom.h b/arch/mips/include/asm/prom.h index 0b4b668..bd0c5fd 100644 --- a/arch/mips/include/asm/prom.h +++ b/arch/mips/include/asm/prom.h @@ -28,6 +28,11 @@ extern int __dt_register_buses(const char *bus0, const char *bus1); static inline void device_tree_init(void) { } #endif /* CONFIG_OF */ +#if defined(CONFIG_MIPS_RAW_APPENDED_DTB) ||\ + defined(CONFIG_MIPS_ZBOOT_APPENDED_DTB) +extern const char __appended_dtb[]; +#endif + extern char *mips_get_machine_name(void); extern void mips_set_machine_name(const char *name); diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S index 56e8fed..766205c 100644 --- a/arch/mips/kernel/head.S +++ b/arch/mips/kernel/head.S @@ -93,22 +93,6 @@ NESTED(kernel_entry, 16, sp) # kernel entry point jr t0 0: -#ifdef CONFIG_MIPS_RAW_APPENDED_DTB - PTR_LA t0, __appended_dtb - -#ifdef CONFIG_CPU_BIG_ENDIAN - li t1, 0xd00dfeed -#else - li t1, 0xedfe0dd0 -#endif - lw t2, (t0) - bne t1, t2, not_found - nop - - move a1, t0 - PTR_LI a0, -2 -not_found: -#endif PTR_LA t0, __bss_start # clear .bss LONG_S zero, (t0) PTR_LA t1, __bss_stop - LONGSIZE diff --git a/arch/mips/lantiq/prom.c b/arch/mips/lantiq/prom.c index 5f693ac..f454b9d 100644 --- a/arch/mips/lantiq/prom.c +++ b/arch/mips/lantiq/prom.c @@ -74,6 +74,13 @@ void __init plat_mem_setup(void) set_io_port_base((unsigned long) KSEG1); +#if defined(CONFIG_MIPS_RAW_APPENDED_DTB) ||\ + defined(CONFIG_MIPS_ZBOOT_APPENDED_DTB) + if (be32_to_cpup((__be32 *)__appended_dtb) == 0xd00dfeed) { + fw_arg0 = -2; + fw_arg1 = (unsigned long)__appended_dtb; + } +#endif if (fw_arg0 == -2) /* UHI interface */ dtb = (void *)fw_arg1; else if (__dtb_start != __dtb_end) -- 1.9.1
