[U-Boot] [PATCH 08/48] x86: Add various minor tidy-ups to the 32-bit startup code

[Bin Meng]

On Wed, Jul 22, 2015 at 11:49 PM, Simon Glass <sjg at chromium.org> wrote:
> Fix a typo, improve some comments and add a little more detail in some
> cases.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  arch/x86/cpu/start.S | 46 ++++++++++++++++++++++++++--------------------
>  1 file 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 */
> --

Reviewed-by: Bin Meng <bmeng.cn at gmail.com>