[coreboot-gerrit] New patch to review for coreboot: arch/x86: Implement minimal bootblock for C_ENVIRONMENT_BOTOBLOCK

[Alexandru Gagniuc (mr.nuke.me@gmail.com)]

Alexandru Gagniuc (mr.nuke.me at gmail.com) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/13485

-gerrit

commit 05000e85df47324cb446bc627203a441ec152b6d
Author: Alexandru Gagniuc <mr.nuke.me at gmail.com>
Date:   Tue Jan 26 18:22:43 2016 -0800

    arch/x86: Implement minimal bootblock for C_ENVIRONMENT_BOTOBLOCK
    
    Some newer x86 systems can boot from non-memory-mapped boot media
    (e.g. EMMC). The bootblock may be backed by small amounts of SRAM, or
    other memory, similar to how most ARM chipsets work. In such cases, we
    may not have enough code space for romstage very early on. This means
    that CAR setup and early boot media (e.g. SPI, EMMC) drivers need to
    be implemented within the limited amount memory of storage available.
    Since the reset vector has to be contained in this early code memory,
    the bootblock is the best place to implement loading of other stages.
    
    Implement a bootblock which does the minimal initialization, up to,
    and including switch to protected mode. This then transfers control
    to platform-specific code. No stack is needed, and control is
    transferred via a "jmp" such that no stack operations are involved.
    
    Change-Id: I009b42b9a707cf11a74493bd4d8c189dc09b8ace
    Signed-off-by: Alexandru Gagniuc <mr.nuke.me at gmail.com>
---
 src/arch/x86/Makefile.inc     |  1 +
 src/arch/x86/bootblock_crt0.S | 56 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/src/arch/x86/Makefile.inc b/src/arch/x86/Makefile.inc
index 6667731..9084b11 100644
--- a/src/arch/x86/Makefile.inc
+++ b/src/arch/x86/Makefile.inc
@@ -112,6 +112,7 @@ $(obj)/arch/x86/id.bootblock.o: $(obj)/build.h
 
 ifeq ($(CONFIG_C_ENVIRONMENT_BOOTBLOCK),y)
 
+bootblock-y += bootblock_crt0.S
 bootblock-y += memlayout.ld
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_X86_32),y)
diff --git a/src/arch/x86/bootblock_crt0.S b/src/arch/x86/bootblock_crt0.S
new file mode 100644
index 0000000..aee5075
--- /dev/null
+++ b/src/arch/x86/bootblock_crt0.S
@@ -0,0 +1,56 @@
+/*
+ * This is the modern bootblock. It is used by platforms which select
+ * C_ENVIRONMENT_BOOTBLOCK, and it prepares the system for C environment runtime
+ * setup. The actual setup is done by hardware-specific code.
+ *
+ * It provides a bootflow similar to other architectures, and thus is considered
+ * to be the modern approach.
+ *
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2015 Alexandru Gagniuc <mr.nuke.me at gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#define CR0_MP		(1 << 1)
+#define CR0_EM		(1 << 2)
+
+#define CR4_OSFXSR	(1 << 9)
+#define CR4_OSXMMEXCPT	(1 << 10)
+
+/*
+ * Include the old code for reset vector and protected mode entry. That code has
+ * withstood the test of time.
+ */
+#include <arch/x86/prologue.inc>
+#include <cpu/x86/16bit/entry16.inc>
+#include <cpu/x86/16bit/reset16.inc>
+#include <cpu/x86/32bit/entry32.inc>
+
+.intel_syntax noprefix
+
+bootblock_protected_mode_entry:
+	/* Save BIST result */
+	movd	mm0, eax
+	/* Save an early timestamp */
+	rdtsc
+	movd	mm1, eax
+	movd	mm2, edx
+
+#if !IS_ENABLED(CONFIG_SSE)
+enable_sse:
+	mov	eax, cr0
+	and	ax, not CR0_EM		/* Clear coprocessor emulation CR0.EM */
+	or	ax, CR0_MP		/* Set coprocessor monitoring  CR0.MP */
+	mov	cr0, eax
+	mov	eax, cr4
+	or	ax, (CR4_OSFXSR | CR4_OSXMMEXCPT)
+	mov	cr4, eax
+#endif /* IS_ENABLED(CONFIG_SSE) */
+
+	/* We're done. Now it's up to platform-specific code */
+	jmp	bootblock_pre_c_entry