diff options
| -rw-r--r-- | arch/x86/cpu/start.S | 46 |
1 files changed, 26 insertions, 20 deletions
diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S index 00e585e..7ef8b88 100644 --- a/arch/x86/cpu/start.S +++ b/arch/x86/cpu/start.S @@ -25,11 +25,11 @@ .globl _x86boot_start _x86boot_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) + * This is the fail-safe 32-bit bootstrap entry point. + * + * This code is used when booting from another boot loader like + * coreboot or EFI. So we repeat some of the same init found in + * start16. */ cli cld @@ -45,15 +45,15 @@ _x86boot_start: jmp 1f _start: /* - * This is the 32-bit cold-reset entry point. Initialize %bx to 0 - * in case we're preceeded by some sort of boot stub. + * This is the 32-bit cold-reset entry point, coming from start16. + * Set %bx to 0 to indicate this. */ movw $GD_FLG_COLD_BOOT, %bx 1: /* Save BIST */ movl %eax, %ebp - /* Load the segement registes to match the gdt loaded in start16.S */ + /* Load the segement registers to match the GDT loaded in start16.S */ movl $(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax movw %ax, %fs movw %ax, %ds @@ -64,7 +64,11 @@ _start: /* Clear the interrupt vectors */ lidt blank_idt_ptr - /* Early platform init (setup gpio, etc ) */ + /* + * Critical early platform init - generally not used, we prefer init + * to happen later when we have a console, in case something goes + * wrong. + */ jmp early_board_init .globl early_board_init_ret early_board_init_ret: @@ -79,7 +83,7 @@ car_init_ret: * We now have CONFIG_SYS_CAR_SIZE bytes of Cache-As-RAM (or SRAM, * or fully initialised SDRAM - we really don't care which) * starting at CONFIG_SYS_CAR_ADDR to be used as a temporary stack - * and early malloc area. The MRC requires some space at the top. + * and early malloc() area. The MRC requires some space at the top. * * Stack grows down from top of CAR. We have: * @@ -97,7 +101,7 @@ car_init_ret: #endif #else /* - * When we get here after car_init, esp points to a temporary stack + * When we get here after car_init(), esp points to a temporary stack * and esi holds the HOB list address returned by the FSP. */ #endif @@ -137,17 +141,18 @@ skip_hob: movl %esp, %ecx #if defined(CONFIG_SYS_MALLOC_F_LEN) + /* Set up the pre-relocation malloc pool */ subl $CONFIG_SYS_MALLOC_F_LEN, %esp movl %eax, %edx addl $GD_MALLOC_BASE, %edx movl %esp, (%edx) #endif - /* Store BIST */ + /* Store BIST into global_data */ movl %eax, %edx addl $GD_BIST, %edx movl %ebp, (%edx) - /* Set second parameter to setup_gdt */ + /* Set second parameter to setup_gdt() */ movl %ecx, %edx /* Setup global descriptor table so gd->xyz works */ @@ -157,7 +162,7 @@ skip_hob: post_code(POST_START_DONE) xorl %eax, %eax - /* Enter, U-boot! */ + /* Enter, U-Boot! */ call board_init_f /* indicate (lack of) progress */ @@ -184,13 +189,13 @@ board_init_f_r_trampoline: /* Align global data to 16-byte boundary */ andl $0xfffffff0, %esp - /* Setup first parameter to memcpy (and setup_gdt) */ + /* Setup first parameter to memcpy() and setup_gdt() */ movl %esp, %eax - /* Setup second parameter to memcpy */ + /* Setup second parameter to memcpy() */ fs movl 0, %edx - /* Set third parameter to memcpy */ + /* Set third parameter to memcpy() */ movl $GENERATED_GBL_DATA_SIZE, %ecx /* Copy global data from CAR to SDRAM stack */ @@ -202,7 +207,7 @@ board_init_f_r_trampoline: /* Align global descriptor table to 16-byte boundary */ andl $0xfffffff0, %esp - /* Set second parameter to setup_gdt */ + /* Set second parameter to setup_gdt() */ movl %esp, %edx /* Setup global descriptor table so gd->xyz works */ @@ -216,7 +221,7 @@ board_init_f_r_trampoline: call car_uninit 1: - /* Re-enter U-Boot by calling board_init_f_r */ + /* Re-enter U-Boot by calling board_init_f_r() */ call board_init_f_r die: @@ -230,9 +235,10 @@ blank_idt_ptr: .p2align 2 /* force 4-byte alignment */ + /* Add a multiboot header so U-Boot can be loaded by GRUB2 */ multiboot_header: /* magic */ - .long 0x1BADB002 + .long 0x1badb002 /* flags */ .long (1 << 16) /* checksum */ |