[ARM] 4736/1: Export atags to userspace and allow kexec to use customised atags

Currently, the atags used by kexec are fixed to the ones originally used
to boot the kernel. This is less than ideal as changing the commandline,
initrd and other options would be a useful feature.

This patch exports the atags used for the current kernel to userspace
through an "atags" file in procfs. The presence of the file is
controlled by its own Kconfig option and cleans up several ifdef blocks
into a separate file. The tags for the new kernel are assumed to be at
a fixed location before the kernel image itself. The location of the
tags used to boot the original kernel is unimportant and no longer
saved.

Based on a patch from Uli Luckas <[e-mail]>

Signed-off-by: Richard Purdie <[e-mail]>
Acked-by: Uli Luckas <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/Kconfig

···
 	  initially work for you.  It may help to enable device hotplugging
 	  support.
 
+config ATAGS_PROC
+	bool "Export atags in procfs"
+	default n
+	help
+	  Should the atags used to boot the kernel be exported in an "atags"
+	  file in procfs. Useful with kexec.
+
 endmenu
 
 if (ARCH_SA1100 || ARCH_INTEGRATOR || ARCH_OMAP || ARCH_IMX || ARCH_PXA)

arch/arm/kernel/Makefile

···
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-decode.o
+obj-$(CONFIG_ATAGS_PROC)	+= atags.o
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
 
 obj-$(CONFIG_CRUNCH)		+= crunch.o crunch-bits.o

arch/arm/kernel/atags.c

···
+#include <linux/slab.h>
+#include <linux/kexec.h>
+#include <linux/proc_fs.h>
+#include <asm/setup.h>
+#include <asm/types.h>
+#include <asm/page.h>
+
+struct buffer {
+	size_t size;
+	char *data;
+};
+static struct buffer tags_buffer;
+
+static int
+read_buffer(char* page, char** start, off_t off, int count,
+	int* eof, void* data)
+{
+	struct buffer *buffer = (struct buffer *)data;
+
+	if (off >= buffer->size) {
+		*eof = 1;
+		return 0;
+	}
+
+	count = min((int) (buffer->size - off), count);
+
+	memcpy(page, &buffer->data[off], count);
+
+	return count;
+}
+
+
+static int
+create_proc_entries(void)
+{
+	struct proc_dir_entry* tags_entry;
+
+	tags_entry = create_proc_read_entry("atags", 0400, &proc_root, read_buffer, &tags_buffer);
+	if (!tags_entry)
+		return -ENOMEM;
+
+	return 0;
+}
+
+
+static char __initdata atags_copy_buf[KEXEC_BOOT_PARAMS_SIZE];
+static char __initdata *atags_copy;
+
+void __init save_atags(const struct tag *tags)
+{
+	atags_copy = atags_copy_buf;
+	memcpy(atags_copy, tags, KEXEC_BOOT_PARAMS_SIZE);
+}
+
+
+static int __init init_atags_procfs(void)
+{
+	struct tag *tag;
+	int error;
+
+	if (!atags_copy) {
+		printk(KERN_WARNING "Exporting ATAGs: No saved tags found\n");
+		return -EIO;
+	}
+
+	for (tag = (struct tag *) atags_copy; tag->hdr.size; tag = tag_next(tag))
+		;
+
+	tags_buffer.size = ((char *) tag - atags_copy) + sizeof(tag->hdr);
+	tags_buffer.data = kmalloc(tags_buffer.size, GFP_KERNEL);
+	if (tags_buffer.data == NULL)
+		return -ENOMEM;
+	memcpy(tags_buffer.data, atags_copy, tags_buffer.size);
+
+	error = create_proc_entries();
+	if (error) {
+		printk(KERN_ERR "Exporting ATAGs: not enough memory\n");
+		kfree(tags_buffer.data);
+		tags_buffer.size = 0;
+		tags_buffer.data = NULL;
+	}
+
+	return error;
+}
+
+arch_initcall(init_atags_procfs);

arch/arm/kernel/atags.h

···
+#ifdef CONFIG_ATAGS_PROC
+extern void save_atags(struct tag *tags);
+#else
+static inline void save_atags(struct tag *tags) { }
+#endif

arch/arm/kernel/machine_kexec.c

···
 extern unsigned long kexec_start_address;
 extern unsigned long kexec_indirection_page;
 extern unsigned long kexec_mach_type;
+extern unsigned long kexec_boot_atags;
 
 /*
  * Provide a dummy crash_notes definition while crash dump arrives to arm.
···
 	kexec_start_address = image->start;
 	kexec_indirection_page = page_list;
 	kexec_mach_type = machine_arch_type;
+	kexec_boot_atags = image->start - KEXEC_ARM_ZIMAGE_OFFSET + KEXEC_ARM_ATAGS_OFFSET;
 
 	/* copy our kernel relocation code to the control code page */
 	memcpy(reboot_code_buffer,

arch/arm/kernel/relocate_kernel.S

···
 	.globl relocate_new_kernel
 relocate_new_kernel:
 
-	/* Move boot params back to where the kernel expects them */
-
-	ldr	r0,kexec_boot_params_address
-	teq	r0,#0
-	beq	8f
-
-	ldr	r1,kexec_boot_params_copy
-	mov	r6,#KEXEC_BOOT_PARAMS_SIZE/4
-7:
-	ldr	r5,[r1],#4
-	str	r5,[r0],#4
-	subs	r6,r6,#1
-	bne	7b
-
-8:
-	/* Boot params moved, now go on with the kernel */
-
 	ldr	r0,kexec_indirection_page
 	ldr	r1,kexec_start_address
 
···
 	mov lr,r1
 	mov r0,#0
 	ldr r1,kexec_mach_type
-	ldr r2,kexec_boot_params_address
+	ldr r2,kexec_boot_atags
 	mov pc,lr
 
 	.globl kexec_start_address
···
 kexec_mach_type:
 	.long	0x0
 
-	/* phy addr where new kernel will expect to find boot params */
-	.globl kexec_boot_params_address
-kexec_boot_params_address:
-	.long	0x0
-
-	/* phy addr where old kernel put a copy of orig boot params */
-	.globl kexec_boot_params_copy
-kexec_boot_params_copy:
+	/* phy addr of the atags for the new kernel */
+	.globl kexec_boot_atags
+kexec_boot_atags:
 	.long	0x0
 
 relocate_new_kernel_end:

arch/arm/kernel/setup.c

···
 #include <linux/interrupt.h>
 #include <linux/smp.h>
 #include <linux/fs.h>
-#include <linux/kexec.h>
 
 #include <asm/cpu.h>
 #include <asm/elf.h>
···
 #include <asm/mach/time.h>
 
 #include "compat.h"
+#include "atags.h"
 
 #ifndef MEM_SIZE
 #define MEM_SIZE	(16*1024*1024)
···
 }
 arch_initcall(customize_machine);
 
-#ifdef CONFIG_KEXEC
-
-/* Physical addr of where the boot params should be for this machine */
-extern unsigned long kexec_boot_params_address;
-
-/* Physical addr of the buffer into which the boot params are copied */
-extern unsigned long kexec_boot_params_copy;
-
-/* Pointer to the boot params buffer, for manipulation and display */
-unsigned long kexec_boot_params;
-EXPORT_SYMBOL(kexec_boot_params);
-
-/* The buffer itself - make sure it is sized correctly */
-static unsigned long kexec_boot_params_buf[(KEXEC_BOOT_PARAMS_SIZE + 3) / 4];
-
-#endif
-
 void __init setup_arch(char **cmdline_p)
 {
 	struct tag *tags = (struct tag *)&init_tags;
···
 	else if (mdesc->boot_params)
 		tags = phys_to_virt(mdesc->boot_params);
 
-#ifdef CONFIG_KEXEC
-	kexec_boot_params_copy = virt_to_phys(kexec_boot_params_buf);
-	kexec_boot_params = (unsigned long)kexec_boot_params_buf;
-	if (__atags_pointer) {
-		kexec_boot_params_address = __atags_pointer;
-		memcpy((void *)kexec_boot_params, tags, KEXEC_BOOT_PARAMS_SIZE);
-	} else if (mdesc->boot_params) {
-		kexec_boot_params_address = mdesc->boot_params;
-		memcpy((void *)kexec_boot_params, tags, KEXEC_BOOT_PARAMS_SIZE);
-	}
-#endif
-
 	/*
 	 * If we have the old style parameters, convert them to
 	 * a tag list.
···
 	if (tags->hdr.tag == ATAG_CORE) {
 		if (meminfo.nr_banks != 0)
 			squash_mem_tags(tags);
+		save_atags(tags);
 		parse_tags(tags);
 	}
 

include/asm-arm/kexec.h

···
 
 #define KEXEC_BOOT_PARAMS_SIZE 1536
 
+#define KEXEC_ARM_ATAGS_OFFSET  0x1000
+#define KEXEC_ARM_ZIMAGE_OFFSET 0x8000
+
 #ifndef __ASSEMBLY__
 
 struct kimage;