[U-Boot] [PATCH] arm: add IPL support

[Kuo-Jung Su <dantesu@gmail.com>]

Initial Program Loader (IPL) usually runs with .text and .rodata
in ROM, while .data and .bss reside in RAM.

This patch uses the AT keyword to specify load address,
and a small code snippet in crt0.S to restore .data section
at runtime.

Example usage:
Assume the target device has a 4KB ROM at 0x00000000 and a
4KB SRAM at 0xA0000000, the IPL/SPL config could be:

#define CONFIG_SPL_MAX_SIZE  0x1000 /* text + data, no bss */
#define CONFIG_SPL_TEXT_BASE 0x00000000
#define CONFIG_SPL_DATA_BASE 0xA0000000
#define CONFIG_SPL_STACK     0xA0001000

Signed-off-by: Kuo-Jung Su <dantesu@gmail.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
---
 README                      |   10 ++++++++++
 arch/arm/cpu/u-boot-spl.lds |   26 ++++++++++++++++++++++++--
 arch/arm/lib/crt0.S         |   22 ++++++++++++++++++++++
 spl/Makefile                |    6 ++++++
 4 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/README b/README
index a8d3039..992064a 100644
--- a/README
+++ b/README
@@ -3094,6 +3094,16 @@ FIT uImage format:
 		Address to relocate to.  If unspecified, this is equal to
 		CONFIG_SPL_TEXT_BASE (i.e. no relocation is done).

+		CONFIG_SPL_DATA_BASE
+		Link address for the .data and .bss within the SPL binary.
+		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_DATA_BASE
+		must not be both defined at the same time.
+
+		CONFIG_SPL_DATA_MAX_SIZE
+		Maximum size in memory allocated to the SPL .data + .bss.
+		When defined, the linker checks that the actual memory used
+		by SPL from __data_start to __bss_end does not exceed it.
+
 		CONFIG_SPL_BSS_START_ADDR
 		Link address for the BSS within the SPL binary.

diff --git a/arch/arm/cpu/u-boot-spl.lds b/arch/arm/cpu/u-boot-spl.lds
index 36cc54a..ea6284f 100644
--- a/arch/arm/cpu/u-boot-spl.lds
+++ b/arch/arm/cpu/u-boot-spl.lds
@@ -26,15 +26,28 @@ SECTIONS
 	.rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) }

 	. = ALIGN(4);
-	.data : {
+
+#if defined(CONFIG_SPL_DATA_BASE)
+	__image_copy_end = .;
+
+	.data : AT ( __image_copy_end )
+#else
+	.data :
+#endif
+	{
+		__data_start = .;
 		*(.data*)
+		. = ALIGN(4);
+		__data_end = .;
 	}

 	. = ALIGN(4);

 	. = .;

+#if !defined(CONFIG_SPL_DATA_BASE)
 	__image_copy_end = .;
+#endif

 	.rel.dyn : {
 		__rel_dyn_start = .;
@@ -59,11 +72,20 @@ SECTIONS
 	/DISCARD/ : { *(.gnu*) }
 }

-#if defined(CONFIG_SPL_MAX_SIZE)
+#if defined(CONFIG_SPL_MAX_SIZE) && defined(CONFIG_SPL_DATA_BASE)
+ASSERT((__image_copy_end - __image_copy_start) + \
+	(__data_end - __data_start) < (CONFIG_SPL_MAX_SIZE), \
+	"SPL image too big");
+#elif defined(CONFIG_SPL_MAX_SIZE)
 ASSERT(__image_copy_end - __image_copy_start < (CONFIG_SPL_MAX_SIZE), \
 	"SPL image too big");
 #endif

+#if defined(CONFIG_SPL_DATA_MAX_SIZE)
+ASSERT(__bss_end - __data_start < (CONFIG_SPL_DATA_MAX_SIZE), \
+	"SPL image DATA plus BSS too big");
+#endif
+
 #if defined(CONFIG_SPL_BSS_MAX_SIZE)
 ASSERT(__bss_end - __bss_start < (CONFIG_SPL_BSS_MAX_SIZE), \
 	"SPL image BSS too big");
diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
index ac54b93..46d0e03 100644
--- a/arch/arm/lib/crt0.S
+++ b/arch/arm/lib/crt0.S
@@ -58,6 +58,28 @@
 ENTRY(_main)

 /*
+ * Restore .data (initialized) section
+ */
+
+#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_DATA_BASE)
+
+	/* Load values from the board-specific linker script. */
+	ldr r0, =__image_copy_end /* source start address */
+	ldr r1, =__data_start
+	ldr r2, =__data_end
+	sub r2, r2, r1
+	add r2, r0, r2            /* source end address   */
+	ldr r1, =CONFIG_SPL_DATA_BASE
+
+data_copy:
+	ldmia r0!, {r3-r10}       /* copy from source address [r0] */
+	stmia r1!, {r3-r10}       /* copy to   target address [r1] */
+	cmp   r0, r2              /* until source end addreee [r2] */
+	blo   data_copy
+
+#endif	/* CONFIG_SPL_BUILD && CONFIG_SPL_DATA_BASE */
+
+/*
  * Set up initial C runtime environment and call board_init_f(0).
  */

diff --git a/spl/Makefile b/spl/Makefile
index 29d7818..540ef8c 100644
--- a/spl/Makefile
+++ b/spl/Makefile
@@ -54,6 +54,12 @@ ifeq ($(CPU),mpc85xx)
 START += $(START_PATH)/resetvec.o
 endif

+ifdef CONFIG_SPL_DATA_BASE
+LDFLAGS += -Ttext $(CONFIG_SPL_TEXT_BASE) -Tdata $(CONFIG_SPL_DATA_BASE)
+else
+LDFLAGS += -Ttext $(CONFIG_SPL_TEXT_BASE)
+endif
+
 LIBS-y += arch/$(ARCH)/lib/

 LIBS-y += $(CPUDIR)/
--
1.7.9.5