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>
diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index 1980f1a..3cea04b 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 @@
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 @@
die: hlt
jmp die
hlt
+
+blank_idt_ptr:
+ .word 0 /* limit */
+ .long 0 /* base */