x86: Use fs for global data

Use the base address of the 'F' segment as a pointer to the global data
structure. By adding the linear address (i.e. the 'D' segment address) as
the first word of the global data structure, the address of the global data
relative to the 'D' segment can be found simply, for example, by:

	fs movl 0, %eax

This makes the gd 'pointer' writable prior to relocation (by reloading the
Global Desctriptor Table) which brings x86 into line with all other arches

NOTE: Writing to the gd 'pointer' is expensive (but we only do it
twice) but using it to access global data members (read and write) is
still fairly cheap

--
Changes for v2:
 - Rebased against changes made to patch #3
 - Removed extra indent
 - Tweaked commit message

3 files changed, 17 insertions, 7 deletions

diff --git a/arch/x86/include/asm/global_data.h b/arch/x86/include/asm/global_data.h
index 05a2139..908a02c 100644
--- a/arch/x86/include/asm/global_data.h
+++ b/arch/x86/include/asm/global_data.h
@@ -36,6 +36,8 @@
 #ifndef __ASSEMBLY__
 
 typedef	struct global_data {
+	/* NOTE: gd_addr MUST be first member of struct global_data! */
+	unsigned long	gd_addr;	/* Location of Global Data */
 	bd_t		*bd;
 	unsigned long	flags;
 	unsigned long	baudrate;
@@ -51,13 +53,24 @@ typedef	struct global_data {
 	unsigned long	bus_clk;
 	unsigned long	relocaddr;	/* Start address of U-Boot in RAM */
 	unsigned long	start_addr_sp;	/* start_addr_stackpointer */
+	unsigned long	gdt_addr;	/* Location of GDT */
+	unsigned long	new_gd_addr;	/* New location of Global Data */
 	phys_size_t	ram_size;	/* RAM size */
 	unsigned long	reset_status;	/* reset status register at boot */
 	void		**jt;		/* jump table */
 	char		env_buf[32];	/* buffer for getenv() before reloc. */
 } gd_t;
 
-extern gd_t *gd;
+static inline gd_t *get_fs_gd_ptr(void)
+{
+	gd_t *gd_ptr;
+
+	asm volatile("fs movl 0, %0\n" : "=r" (gd_ptr));
+
+	return gd_ptr;
+}
+
+#define gd	get_fs_gd_ptr()
 
 #endif
 
@@ -73,12 +86,6 @@ extern gd_t *gd;
 #define GD_FLG_DISABLE_CONSOLE	0x00040	/* Disable console (in & out)		*/
 #define GD_FLG_ENV_READY	0x00080	/* Environment imported into hash table	*/
 
-#if 0
 #define DECLARE_GLOBAL_DATA_PTR
-#else
-#define XTRN_DECLARE_GLOBAL_DATA_PTR    extern
-#define DECLARE_GLOBAL_DATA_PTR     XTRN_DECLARE_GLOBAL_DATA_PTR \
-gd_t *gd
-#endif
 
 #endif /* __ASM_GBL_DATA_H */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index aa8188e..6eb5180 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -33,6 +33,7 @@ enum {
 	X86_GDT_ENTRY_UNUSED,
 	X86_GDT_ENTRY_32BIT_CS,
 	X86_GDT_ENTRY_32BIT_DS,
+	X86_GDT_ENTRY_32BIT_FS,
 	X86_GDT_ENTRY_16BIT_CS,
 	X86_GDT_ENTRY_16BIT_DS,
 	X86_GDT_NUM_ENTRIES
diff --git a/arch/x86/include/asm/u-boot-x86.h b/arch/x86/include/asm/u-boot-x86.h
index c3d2277..5540d51 100644
--- a/arch/x86/include/asm/u-boot-x86.h
+++ b/arch/x86/include/asm/u-boot-x86.h
@@ -37,6 +37,8 @@ int x86_cpu_init_r(void);
 int cpu_init_r(void);
 int x86_cpu_init_f(void);
 int cpu_init_f(void);
+void init_gd(gd_t *id, u64 *gdt_addr);
+void setup_gdt(gd_t *id, u64 *gdt_addr);
 
 /* cpu/.../timer.c */
 void timer_isr(void *);