[ARM] 4599/1: Preserve ATAG list for use with kexec (2.6.23)

This patch resolves a kexec boot failure that can occur because
no ATAGs are passed in to the kexec'd kernel. Currently the
newly-kexec'd kernel may fail if it requires specific ATAGs, or
it may fail because the fixed memory location at which it expects
to find the ATAGs may contain random data instead of ATAGs.

The patch ensures that any ATAGs passed to the current kernel
at boot time are copied to a static buffer, and are copied back
when kexec copies the new kernel into place. Thus the new
kernel sees the same ATAGs from kexec and the boot loader.

The boot parameters are copied without regard to type, content,
or length -- this patch's scope is limited soley to saving and
restoring a fixed-size block of memory containing the kernel's
boot parameters. Additional functionality to examine, alter, or
replace the ATAGs (using kexec, for example) can be implemented
by manipulating the static buffer containing the preserved ATAGs.

Note: the size of the buffer (1.5KB) is selected to comfortably
hold one of each ATAG type, including a maximum-length command
line and the maximum number of ATAG_MEM structures currently
supported by the kernel. Should an ATAG list exceed that limit,
the list will be silently truncated to that limit (to do other-
wise at that point in the boot process would make a simple
problem exceedingly complicated).

[Note: this is the same patch as 4579, modified to accomodate
the ATAG changes introduced in 2.6.23]

Signed-off-by: Mike Westerhof <mwester at dls.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/relocate_kernel.S

@@ -7,6 +7,23 @@
 	.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
 
@@ -50,7 +67,7 @@ relocate_new_kernel:
 	mov lr,r1
 	mov r0,#0
 	ldr r1,kexec_mach_type
-	mov r2,#0
+	ldr r2,kexec_boot_params_address
 	mov pc,lr
 
 	.globl kexec_start_address
@@ -65,6 +82,16 @@ kexec_indirection_page:
 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:
+	.long	0x0
+
 relocate_new_kernel_end:
 
 	.globl relocate_new_kernel_size

arch/arm/kernel/setup.c

@@ -24,6 +24,7 @@
 #include <linux/interrupt.h>
 #include <linux/smp.h>
 #include <linux/fs.h>
+#include <linux/kexec.h>
 
 #include <asm/cpu.h>
 #include <asm/elf.h>
@@ -783,6 +784,23 @@ static int __init customize_machine(void)
 }
 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;
@@ -801,6 +819,18 @@ void __init setup_arch(char **cmdline_p)
 	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.

include/asm-arm/kexec.h

@@ -14,6 +14,8 @@
 
 #define KEXEC_ARCH KEXEC_ARCH_ARM
 
+#define KEXEC_BOOT_PARAMS_SIZE 1536
+
 #ifndef __ASSEMBLY__
 
 struct kimage;