x86: Add RAM bootstrap functionality

[karo-tx-uboot.git] / arch / i386 / cpu / start.S

diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index 25d32e658e60206915ff33573386eb4bdb0548e2..3cea04b4ce37bd480ada911f610d9a800e9255b4 100644 (file)
--- 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 */
@@ -63,6 +95,11 @@ early_board_init_ret:
        jmp     mem_init
 mem_init_ret:
 
+       /* fetch memory size (into %eax) */
+       mov     $get_mem_size_ret, %ebp
+       jmp     get_mem_size
+get_mem_size_ret:
+
        /* Check we have enough memory for stack */
        movl    $CONFIG_SYS_STACK_SIZE, %ecx
        cmpl    %ecx, %eax
@@ -133,3 +170,7 @@ stack_ok:
 die:   hlt
        jmp     die
        hlt
+
+blank_idt_ptr:
+       .word   0               /* limit */
+       .long   0               /* base */