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authorGraeme Russ <graeme.russ@gmail.com>2010-04-24 00:05:42 +1000
committerWolfgang Denk <wd@denx.de>2010-05-06 00:15:31 +0200
commit077e1958ca4afe12d88043b123ded058c51b89f7 (patch)
treeda450fd1e80c401a87d3de1d3a8fe21075e851f3 /arch/i386
parent759598f82f02cc84614450807cb5de43ca18a339 (diff)
downloadu-boot-linaro-stable-077e1958ca4afe12d88043b123ded058c51b89f7.tar.gz
x86: Add RAM bootstrap functionality
Add a parameter to the 32-bit entry to indicate if entry is from Real Mode or not. If entry is from Real Mode, execute the destructive 'sizer' routine to determine memory size as we are booting cold and running in Flash. If not entering from Real Mode, we are executing a U-Boot image from RAM and therefore the memory size is already known (and running 'sizer' will destroy the running image) There are now two 32-bit entry points. The first is the 'in RAM' entry point which exists at the start of the U-Boot binary image. As such, you can load u-boot.bin in RAM and jump directly to the load address without needing to calculate any offsets. The second entry point is used by the real-to-protected mode switch This patch also changes TEXT_BASE to 0x6000000 (in RAM). You can load the resulting image at 0x6000000 and simple go 0x6000000 from the u-boot prompt Hopefully a later patch will completely elliminate any dependency on TEXT_BASE like a relocatable linux kernel (perfect world) Signed-off-by: Graeme Russ <graeme.russ@gmail.com>
Diffstat (limited to 'arch/i386')
-rw-r--r--arch/i386/cpu/start.S36
-rw-r--r--arch/i386/cpu/start16.S8
2 files changed, 38 insertions, 6 deletions
diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index 1980f1a7b..3cea04b4c 100644
--- a/arch/i386/cpu/start.S
+++ b/arch/i386/cpu/start.S
@@ -33,7 +33,27 @@
.type _start, @function
.globl _i386boot_start
_i386boot_start:
+ /*
+ * This is the fail safe 32-bit bootstrap entry point. The
+ * following code is not executed from a cold-reset (actually, a
+ * lot of it is, but from real-mode after cold reset. It is
+ * repeated here to put the board into a state as close to cold
+ * reset as necessary)
+ */
+ cli
+ cld
+
+ /* Turn of cache (this might require a 486-class CPU) */
+ movl %cr0, %eax
+ orl $0x60000000,%eax
+ movl %eax, %cr0
+ wbinvd
+
+ /* Tell 32-bit code it is being entered from an in-RAM copy */
+ movw $0x0000, %bx
_start:
+ /* This is the 32-bit cold-reset entry point */
+
movl $0x18,%eax /* Load our segement registes, the
* gdt have already been loaded by start16.S */
movw %ax,%fs
@@ -42,6 +62,18 @@ _start:
movw %ax,%es
movw %ax,%ss
+ /* Clear the interupt vectors */
+ lidt blank_idt_ptr
+
+ /*
+ * Skip low-level board and memory initialization if not starting
+ * from cold-reset. This allows us to do a fail safe boot-strap
+ * into a new build of U-Boot from a known-good boot flash
+ */
+ movw $0x0001, %ax
+ cmpw %ax, %bx
+ jne mem_init_ret
+
/* We call a few functions in the board support package
* since we have no stack yet we'll have to use %ebp
* to store the return address */
@@ -138,3 +170,7 @@ stack_ok:
die: hlt
jmp die
hlt
+
+blank_idt_ptr:
+ .word 0 /* limit */
+ .long 0 /* base */
diff --git a/arch/i386/cpu/start16.S b/arch/i386/cpu/start16.S
index 1ebb6bc8b..5e33aa106 100644
--- a/arch/i386/cpu/start16.S
+++ b/arch/i386/cpu/start16.S
@@ -45,10 +45,8 @@ board_init16_ret:
wbinvd
/* load the descriptor tables */
-o32 cs lidt idt_ptr
o32 cs lgdt gdt_ptr
-
/* Now, we enter protected mode */
movl %cr0, %eax
orl $1,%eax
@@ -57,6 +55,8 @@ o32 cs lgdt gdt_ptr
/* Flush the prefetch queue */
jmp ff
ff:
+ /* Tell 32-bit code it is being entered from hard-reset */
+ movw $0x0001, %bx
/* Finally jump to the 32bit initialization code */
movw $code32start, %ax
@@ -68,10 +68,6 @@ code32start:
.long _start /* offset */
.word 0x10 /* segment */
-idt_ptr:
- .word 0 /* limit */
- .long 0 /* base */
-
gdt_ptr:
.word 0x30 /* limit (48 bytes = 6 GDT entries) */
.long BOOT_SEG + gdt /* base */