[U-Boot] RFC: Aligning arch initialisation sequences

[Graeme Russ <graeme.russ@gmail.com>]

On 15/11/10 07:05, Albert ARIBAUD wrote:
> Le 14/11/2010 20:34, Graeme Russ a ?crit :
>> On 15/11/10 06:23, Wolfgang Denk wrote:
>>> Dear Albert ARIBAUD,
>>>
>>> In message<4CE0221A.7030502@free.fr>  you wrote:
>>>>
>>>> Alright, then I think we should document how we comply, or do not
>>>> comply, with GNU EABI / AAPCS (maybe a README.arm that people could read
>>>> up) -- and I think if there is a way to access GD both before and after
>>>> relocation without making a register unavailable to the whole u-boot
>>>> code, then we should use it.
>>>
>>> By the way - it should be not difficult to use a normal extern pointer
>>> to reference the global data; see
>>> "arch/powerpc/include/asm/global_data.h":
>>>
>>> 194 #if 1
>>> 195 #define DECLARE_GLOBAL_DATA_PTR     register volatile gd_t *gd asm
>>> ("r2")
>>> 196 #else /* We could use plain global data, but the resulting code is
>>> bigger */
>>> 197 #define XTRN_DECLARE_GLOBAL_DATA_PTR    extern
>>> 198 #define DECLARE_GLOBAL_DATA_PTR     XTRN_DECLARE_GLOBAL_DATA_PTR \
>>> 199                                     gd_t *gd
>>> 200 #endif
>>
>> I think you will find this peculiar to PowerPC
> 
> I don't think Wolfgang's idea is actually processor-specific.
> 
> Each processor has a way to define globals, which end up in the initialized
> data or bss area. BSS is not available before relocation, but initialized
> data is, and remains so after relocation.
> 
> So if we define gd as an initialized pointer (residing in the initialized
> data area), it will be available both before and after relocation.
> 
> Before relocation, this pointer will be read-only. We can set it at compile
> time if we know for each arch (or board) a good address in RAM or IRAM
> where gd can exist.
> 
> After relocation, the pointer becomes read-write: we can copy gd content
> from (I)RAM to RAM if necessary and then update the gd pointer.
> 
>> What you are talking about is exactly how x86 defines gd, but for x86, gd
>> is not accessible until after relocation
> 
> Could it become accessible with the idea I expose above?
> 

Yes - The following patch uses CONFIG_SYS_INIT_SP_ADDR as a temporary
global data area which is copied to a permanent global data structure
located in the data section.

I honestly don't know where I stand on this solution though. By using FS, I
can emulate the 'global register variable' and the initial global data
structure can end up anywhere it needs to be without needing to define
CONFIG_SYS_INIT_SP_ADDR but it will involve self-modifying code I would
prefer not to re-introduce.

However, this method requires CONFIG_SYS_INIT_SP_ADDR which is casting a
certain memory location (in RAM) in stone. Now the eNET has some battery
backed SRAM on board which I can point CONFIG_SYS_INIT_SP_ADDR. So I could
move SDRAM initialisation into C code, but this is not guaranteed for every
x86 board (and for the eNET, it reduces the amount of battery-backed
configuration memory available). I am looking to port U-Boot to a VIA EPIA
EN15000 single board computer. This has no SRAM.

The VIA board has a C7 processor which coreboot has a 'Cache-as-RAM' (CAR)
implementation for, and the SC520 might support CAR (still looking). If
this is the case, I think I can unequivocally support the solution based on
CONFIG_SYS_INIT_SP_ADDR and move low-level init into board_init_f() in line
with the other arches.

For now, consider it a +0.5 vote for the patch below :)

Regards,

Graeme

commit e38af43f0246335578b8c207e8097fd0c5fca520
Author: Graeme Russ <graeme.russ@gmail.com>
Date:   Mon Nov 15 21:15:52 2010 +1100

    x86 Global Data Mods

diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index aaf9dba..4c04a5a 100644
--- a/arch/i386/cpu/start.S
+++ b/arch/i386/cpu/start.S
@@ -127,14 +127,14 @@ mem_ok:
 	/* Set the upper memory limit parameter */
 	subl	$CONFIG_SYS_STACK_SIZE, %eax

-	/* Reserve space for global data */
-	subl	$(GD_SIZE * 4), %eax
-
-	/* %eax points to the global data structure */
+	/* Load some required values into the global data structure */
+	movl	$CONFIG_SYS_INIT_SP_ADDR, %eax
 	movl	%esp, (GD_RAM_SIZE * 4)(%eax)
-	movl	%ebx, (GD_FLAGS * 4)(%eax)
 	movl	%ecx, (GD_LOAD_OFF * 4)(%eax)

+	/* Setup bootflags parameter to board_init_f() */
+	movl	%ebx, %eax
+
 	call	board_init_f	/* Enter, U-boot! */

 	/* indicate (lack of) progress */
diff --git a/arch/i386/include/asm/global_data.h
b/arch/i386/include/asm/global_data.h
index e9000c3..03ecc3c 100644
--- a/arch/i386/include/asm/global_data.h
+++ b/arch/i386/include/asm/global_data.h
@@ -88,6 +88,12 @@ extern gd_t *gd;
 #define GD_FLG_WARM_BOOT	0x00200	/* Warm Boot */


+#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/i386/lib/board.c b/arch/i386/lib/board.c
index 1a962d3..11e6569 100644
--- a/arch/i386/lib/board.c
+++ b/arch/i386/lib/board.c
@@ -45,7 +45,24 @@
 #include <miiphy.h>
 #endif

-DECLARE_GLOBAL_DATA_PTR;
+#if 1 /* We could use plain global data, but the resulting code is bigger */
+/*
+ * Pointer to initial global data area
+ *
+ * Here we initialize it.
+ */
+#undef	XTRN_DECLARE_GLOBAL_DATA_PTR
+#define XTRN_DECLARE_GLOBAL_DATA_PTR	/* empty = allocate here */
+DECLARE_GLOBAL_DATA_PTR = (gd_t *) (CONFIG_SYS_INIT_SP_ADDR);
+#endif  /* 0 */
+
+static inline gd_t *get_gd_ptr(void)
+{
+	gd_t *gd_ptr;
+
+	asm volatile("gs mov 0, %0\n" : "=r" (gd_ptr));
+	return gd_ptr;
+}

 /* Exports from the Linker Script */
 extern ulong __text_start;
@@ -163,12 +180,10 @@ init_fnc_t *init_sequence[] = {
 	NULL,
 };

-gd_t *gd;
-
 /*
  * Load U-Boot into RAM, initialize BSS, perform relocation adjustments
  */
-void board_init_f (ulong gdp)
+void board_init_f (ulong bootflag)
 {
 	void *text_start = &__text_start;
 	void *data_end = &__data_end;
@@ -186,12 +201,14 @@ void board_init_f (ulong gdp)
 	Elf32_Rel *re_src;
 	Elf32_Rel *re_end;

+	gd->flags = bootflag;
+
 	/* Calculate destination RAM Address and relocation offset */
-	dest_addr  = (void *)gdp - (bss_end - text_start);
+	dest_addr  = (void *)gd->ram_size - (bss_end - text_start);
 	rel_offset = dest_addr - text_start;

 	/* Perform low-level initialization only when cold booted */
-	if (((gd_t *)gdp)->flags & GD_FLG_COLD_BOOT) {
+	if (gd->flags & GD_FLG_COLD_BOOT) {
 		/* First stage CPU initialization */
 		if (cpu_init_f() != 0)
 			hang();
@@ -203,8 +220,8 @@ void board_init_f (ulong gdp)

 	/* Copy U-Boot into RAM */
 	dst_addr = (ulong *)dest_addr;
-	src_addr = (ulong *)(text_start + ((gd_t *)gdp)->load_off);
-	end_addr = (ulong *)(data_end  + ((gd_t *)gdp)->load_off);
+	src_addr = (ulong *)(text_start + gd->load_off);
+	end_addr = (ulong *)(data_end  + gd->load_off);

 	while (src_addr < end_addr)
 		*dst_addr++ = *src_addr++;
@@ -217,8 +234,8 @@ void board_init_f (ulong gdp)
 		*dst_addr++ = 0x00000000;

 	/* Perform relocation adjustments */
-	re_src = (Elf32_Rel *)(rel_dyn_start + ((gd_t *)gdp)->load_off);
-	re_end = (Elf32_Rel *)(rel_dyn_end + ((gd_t *)gdp)->load_off);
+	re_src = (Elf32_Rel *)(rel_dyn_start + gd->load_off);
+	re_end = (Elf32_Rel *)(rel_dyn_end + gd->load_off);

 	do {
 		if (re_src->r_offset >= CONFIG_SYS_TEXT_BASE)
@@ -226,11 +243,11 @@ void board_init_f (ulong gdp)
 				*(Elf32_Addr *)(re_src->r_offset + rel_offset) += rel_offset;
 	} while (re_src++ < re_end);

-	((gd_t *)gdp)->reloc_off = rel_offset;
-	((gd_t *)gdp)->flags |= GD_FLG_RELOC;
+	gd->reloc_off = rel_offset;
+	gd->flags |= GD_FLG_RELOC;

 	/* Enter the relocated U-Boot! */
-	(board_init_r + rel_offset)((gd_t *)gdp, (ulong)dest_addr);
+	(board_init_r + rel_offset)(gd, (ulong)dest_addr);

 	/* NOTREACHED - board_init_f() does not return */
 	while(1);
@@ -242,11 +259,15 @@ void board_init_r(gd_t *id, ulong dest_addr)
 	int i;
 	ulong size;
 	static bd_t bd_data;
+	static gd_t static_gd;
+
 	init_fnc_t **init_fnc_ptr;

 	show_boot_progress(0x21);

-	gd = id;
+	memcpy (&static_gd, id, sizeof static_gd);
+	gd = &static_gd;
+
 	/* compiler optimization barrier needed for GCC >= 3.4 */
 	__asm__ __volatile__("": : :"memory");

diff --git a/include/configs/eNET.h b/include/configs/eNET.h
index a04cc9a..b821e2d 100644
--- a/include/configs/eNET.h
+++ b/include/configs/eNET.h
@@ -172,6 +172,7 @@
  * Memory organization
  */
 #define CONFIG_SYS_STACK_SIZE		0x8000  	/* Size of bootloader stack */
+#define CONFIG_SYS_INIT_SP_ADDR		0x1000000
 #define CONFIG_SYS_BL_START_FLASH	0x38040000	/* Address of relocated code */
 #define CONFIG_SYS_BL_START_RAM		0x03fd0000	/* Address of relocated code */
 #define CONFIG_SYS_MONITOR_BASE		CONFIG_SYS_TEXT_BASE