x86: Add various minor tidy-ups to the 32-bit startup code

Fix a typo, improve some comments and add a little more detail in some
cases.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

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 */