[U-Boot] [PATCH] arm: spl: Allow board_init_r() to run with a larger stack

[Simon Glass]

At present SPL uses a single stack, either CONFIG_SPL_STACK or
CONFIG_SYS_INIT_SP_ADDR. Since some SPL features (such as MMC and
environment) require a lot of stack, some boards set CONFIG_SPL_STACK to
point into SDRAM. They then set up SDRAM very early, before board_init_f(),
so that the larger stack can be used.

This is an abuse of lowlevel_init(). That function should only be used for
essential start-up code which cannot be delayed. An example of a valid use is
when only part of the SPL code is visible/executable, and the SoC must be set
up so that board_init_f() can be reached. It should not be used for SDRAM
init, console init, etc.

Add a CONFIG_SPL_STACK_R option, which allows the stack to be moved to a new
address before board_init_r() is called in SPL.

The expected SPL flow (for CONFIG_SPL_FRAMEWORK) is now:

Execution starts with start.S. Two main functions can be provided by the
board implementation. The purpose and limitations of each is described below.
After that, the common board_init_r() is called to perform the SPL task.

lowlevel_init():
	- purpose: essential init to permit execution to reach board_init_f()
	- no global_data, but there is a stack
	- must not set up SDRAM or use console
	- must only do the bare minimum to allow execution to continue to
		board_init_f()
	- this is almost never needed
	- return normally from this function

board_init_f():
	- purpose: set up the machine ready for running board_init_r():
		i.e. SDRAM and serial UART
	- global_data is available
	- preloader_console_init() can be called here in extremis
	- stack is in SRAM
	- should set up SDRAM, and anything needed to make the UART work
	- these is no need to clear BSS, it will be done by crt0.S
	- must return normally from this function (don't call board_init_r()
		directly)

Here the BSS is cleared. If CONFIG_SPL_STACK_R is defined, then at this point
the stack and global_data are relocated to below that address.

board_init_r():
	- purpose: main execution, common code
	- global_data is available
	- SDRAM is available
	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
		points into SDRAM
	- preloader_console_init() can be called here - typically this is
		done by defining CONFIG_SPL_BOARD_INIT and then supplying a
		spl_board_init() function containing this call
	- loads U-Boot or (in falcon mode) Linux

Note: This patch is intended to apply over the top of Tom's SPL changes and
this series:

https://patchwork.ozlabs.org/patch/423785/

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 arch/arm/lib/crt0.S | 13 ++++++++++---
 common/spl/spl.c    | 35 +++++++++++++++++++++++++++++++++++
 doc/README.SPL      | 42 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 87 insertions(+), 3 deletions(-)

diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
index 22df3e5..7939ced 100644
--- a/arch/arm/lib/crt0.S
+++ b/arch/arm/lib/crt0.S
@@ -113,7 +113,14 @@ here:
 /* Set up final (full) environment */
 
 	bl	c_runtime_cpu_setup	/* we still call old routine here */
-
+#endif
+#if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)
+# ifdef CONFIG_SPL_BUILD
+	/* Use a DRAM stack for the rest of SPL, if requested */
+	bl	spl_relocate_stack_gd
+	cmp	r0, #0
+	movne	sp, r0
+# endif
 	ldr	r0, =__bss_start	/* this is auto-relocated! */
 	ldr	r1, =__bss_end		/* this is auto-relocated! */
 
@@ -124,9 +131,10 @@ clbss_l:cmp	r0, r1			/* while not at end of BSS */
 	addlo	r0, r0, #4		/* move to next */
 	blo	clbss_l
 
+#if ! defined(CONFIG_SPL_BUILD)
 	bl coloured_LED_init
 	bl red_led_on
-
+#endif
 	/* call board_init_r(gd_t *id, ulong dest_addr) */
 	mov     r0, r9                  /* gd_t */
 	ldr	r1, [r9, #GD_RELOCADDR]	/* dest_addr */
@@ -134,7 +142,6 @@ clbss_l:cmp	r0, r1			/* while not at end of BSS */
 	ldr	pc, =board_init_r	/* this is auto-relocated! */
 
 	/* we should not return here. */
-
 #endif
 
 ENDPROC(_main)
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 1826c47..78bb279 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -276,3 +276,38 @@ void preloader_console_init(void)
 	spl_display_print();
 #endif
 }
+
+/**
+ * spl_relocate_stack_gd() - Relocate stack ready for board_init_r() execution
+ *
+ * Sometimes board_init_f() runs with a stack in SRAM but we want to use SDRAM
+ * for the main board_init_r() execution. This is typically because we need
+ * more stack space for things like the MMC sub-system.
+ *
+ * This function calculates the stack position, copies the global_data into
+ * place and returns the new stack position. The caller is responsible for
+ * setting up the sp register.
+ *
+ * @return new stack location, or 0 to use the same stack
+ */
+ulong spl_relocate_stack_gd(void)
+{
+#ifdef CONFIG_SPL_STACK_R
+	gd_t *new_gd;
+	ulong ptr;
+
+	/* Get stack position: use 8-byte alignment for ABI compliance */
+	ptr = CONFIG_SPL_STACK_R - sizeof(gd_t);
+	ptr &= ~7;
+	new_gd = (gd_t *)ptr;
+	memcpy(new_gd, (void *)gd, sizeof(gd_t));
+	gd = new_gd;
+
+	/* Clear the BSS. */
+	memset(__bss_start, 0, __bss_end - __bss_start);
+
+	return ptr;
+#else
+	return 0;
+#endif
+}
diff --git a/doc/README.SPL b/doc/README.SPL
index 3ba313c..327d3e2 100644
--- a/doc/README.SPL
+++ b/doc/README.SPL
@@ -95,3 +95,45 @@ cflow will spit out a number of warnings as it does not parse
 the config files and picks functions based on #ifdef.  Parsing the '.i'
 files instead introduces another set of headaches.  These warnings are
 not usually important to understanding the flow, however.
+
+
+ARM SPL Control Flow
+--------------------
+
+Execution starts with start.S. Two main functions can be provided by the
+board implementation. The purpose and limitations of each is described below.
+After that, the common board_init_r() is called to perform the SPL task.
+
+lowlevel_init():
+	- purpose: essential init to permit execution to reach board_init_f()
+	- no global_data, but there is a stack
+	- must not set up SDRAM or use console
+	- must only do the bare minimum to allow execution to continue to
+		board_init_f()
+	- this is almost never needed
+	- return normally from this function
+
+board_init_f():
+	- purpose: set up the machine ready for running board_init_r():
+		i.e. SDRAM and serial UART
+	- global_data is available
+	- preloader_console_init() can be called here in extremis
+	- stack is in SRAM
+	- should set up SDRAM, and anything needed to make the UART work
+	- these is no need to clear BSS, it will be done by crt0.S
+	- must return normally from this function (don't call board_init_r()
+		directly)
+
+Here the BSS is cleared. If CONFIG_SPL_STACK_R is defined, then at this point
+the stack and global_data are relocated to below that address.
+
+board_init_r():
+	- purpose: main execution, common code
+	- global_data is available
+	- SDRAM is available
+	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
+		points into SDRAM
+	- preloader_console_init() can be called here - typically this is
+		done by defining CONFIG_SPL_BOARD_INIT and then supplying a
+		spl_board_init() function containing this call
+	- loads U-Boot or (in falcon mode) Linux
-- 
2.2.0.rc0.207.ga3a616c