x86: Add support for starting from SPL/TPL

When a previous phase of U-Boot has run we need to adjust the init of
subsequent states to avoid messing up the CPU state.

Add a new version of the start logic for SPL, when it boots from TPL
(start_from tpl.c) and a new version for U-Boot when it boots from SPL.

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

1 files changed, 49 insertions, 0 deletions

diff --git a/arch/x86/cpu/start_from_tpl.S b/arch/x86/cpu/start_from_tpl.S
new file mode 100644
index 0000000000..44b5363a68
--- /dev/null
+++ b/arch/x86/cpu/start_from_tpl.S
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * 32-bit x86 Startup Code when running from TPL
+ *
+ * Copyright 2018 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ */
+
+#include <config.h>
+
+.section .text.start
+.code32
+.globl _start
+.type _start, @function
+_start:
+	/* Set up memory using the existing stack */
+	mov	%esp, %eax
+	call	board_init_f_alloc_reserve
+	mov	%eax, %esp
+
+	call	board_init_f_init_reserve
+
+	xorl	%eax, %eax
+	call	board_init_f
+	call	board_init_f_r
+
+	/* Should not return here */
+	jmp	.
+
+.globl board_init_f_r_trampoline
+.type board_init_f_r_trampoline, @function
+board_init_f_r_trampoline:
+	/*
+	 * TPL has been executed: SDRAM has been initialised, BSS has been
+	 * cleared.
+	 *
+	 * %eax = Address of top of new stack
+	 */
+
+	/* Stack grows down from top of SDRAM */
+	movl	%eax, %esp
+
+	/* Re-enter SPL by calling board_init_f_r() */
+	call	board_init_f_r
+
+die:
+	hlt
+	jmp	die
+	hlt