ARM: mxs: Receive r0 and r1 passed from BootROM

Make sure value in register r0 and r1 is preserved and passed to
the board_init_ll() and mxs_common_spl_init() where it can be
processed further. The value in r0 can be configured during the
BootStream generation to arbitary value, r1 contains pointer to
return value from CALL'd function.

This patch also clears the value in r0 before returning to BootROM
to make sure the BootROM is not confused by this value.

Finally, this patch cleans up some comments in the start.S file.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>

3 files changed, 36 insertions, 24 deletions

diff --git a/arch/arm/cpu/arm926ejs/mxs/spl_boot.c b/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
index 0392afd..68c30af 100644
--- a/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
+++ b/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
@@ -102,8 +102,9 @@ static uint8_t mxs_get_bootmode_index(void)
 	return i;
 }
 
-void mxs_common_spl_init(const iomux_cfg_t *iomux_setup,
-			const unsigned int iomux_size)
+void mxs_common_spl_init(const uint32_t arg, const uint32_t *resptr,
+			 const iomux_cfg_t *iomux_setup,
+			 const unsigned int iomux_size)
 {
 	struct mxs_spl_data *data = (struct mxs_spl_data *)
 		((CONFIG_SYS_TEXT_BASE - sizeof(struct mxs_spl_data)) & ~0xf);
diff --git a/arch/arm/cpu/arm926ejs/mxs/start.S b/arch/arm/cpu/arm926ejs/mxs/start.S
index 94b2b3f..3e454ae 100644
--- a/arch/arm/cpu/arm926ejs/mxs/start.S
+++ b/arch/arm/cpu/arm926ejs/mxs/start.S
@@ -152,39 +152,49 @@ _reset:
 	/*
 	 * Store all registers on old stack pointer, this will allow us later to
 	 * return to the BootROM and let the BootROM load U-Boot into RAM.
+	 *
+	 * WARNING: Register r0 and r1 are used by the BootROM to pass data
+	 *          to the called code. Register r0 will contain arbitrary
+	 *          data that are set in the BootStream. In case this code
+	 *          was started with CALL instruction, register r1 will contain
+	 *          pointer to the return value this function can then set.
+	 *          The code below MUST NOT CHANGE register r0 and r1 !
 	 */
 	push	{r0-r12,r14}
 
-	/* save control register c1 */
-	mrc	p15, 0, r0, c1, c0, 0
-	push	{r0}
+	/* Save control register c1 */
+	mrc	p15, 0, r2, c1, c0, 0
+	push	{r2}
 
-	/*
-	 * set the cpu to SVC32 mode and store old CPSR register content
-	 */
-	mrs	r0,cpsr
-	push	{r0}
-	bic	r0,r0,#0x1f
-	orr	r0,r0,#0xd3
-	msr	cpsr,r0
+	/* Set the cpu to SVC32 mode and store old CPSR register content. */
+	mrs	r2, cpsr
+	push	{r2}
+	bic	r2, r2, #0x1f
+	orr	r2, r2, #0xd3
+	msr	cpsr, r2
 
 	bl	board_init_ll
 
+	/* Restore BootROM's CPU mode (especially FIQ). */
+	pop	{r2}
+	msr	cpsr,r2
+
 	/*
-	 * restore bootrom's cpu mode (especially FIQ)
+	 * Restore c1 register. Especially set exception vector location
+	 * back to BootROM space which is required by bootrom for USB boot.
 	 */
-	pop	{r0}
-	msr	cpsr,r0
+	pop	{r2}
+	mcr	p15, 0, r2, c1, c0, 0
+
+	pop	{r0-r12,r14}
 
 	/*
-	 * restore c1 register
-	 * (especially set exception vector location back to
-	 * bootrom space which is required by bootrom for USB boot)
+	 * In case this code was started by the CALL instruction, the register
+	 * r0 is examined by the BootROM after this code returns. The value in
+	 * r0 must be set to 0 to indicate successful return.
 	 */
-	pop	{r0}
-	mcr	p15, 0, r0, c1, c0, 0
+	mov r0, #0
 
-	pop	{r0-r12,r14}
 	bx	lr
 
 _hang:
diff --git a/arch/arm/include/asm/arch-mxs/sys_proto.h b/arch/arm/include/asm/arch-mxs/sys_proto.h
index 1038592..43c7dd6 100644
--- a/arch/arm/include/asm/arch-mxs/sys_proto.h
+++ b/arch/arm/include/asm/arch-mxs/sys_proto.h
@@ -28,8 +28,9 @@ int mxsmmc_initialize(bd_t *bis, int id, int (*wp)(int), int (*cd)(int));
 #include <asm/arch/iomux-mx28.h>
 #endif
 
-void mxs_common_spl_init(const iomux_cfg_t *iomux_setup,
-			const unsigned int iomux_size);
+void mxs_common_spl_init(const uint32_t arg, const uint32_t *resptr,
+			 const iomux_cfg_t *iomux_setup,
+			 const unsigned int iomux_size);
 #endif
 
 struct mxs_pair {