[U-Boot] [PATCH 1/2] sunxi: Use Thumb2 and move stack to gain more SRAM space in FEL mode

[Hans de Goede]

Hi,

On 07/18/2014 07:09 PM, Siarhei Siamashka wrote:
> The Allwinner SoCs support a special FEL boot mode, which can be activated
> by users via a button press (or other means). In the FEL mode, the BROM
> implements a custom FEL protocol over USB, which allows to upload code to
> the device and run it. This protocol had been reverse engineered and
> documented by Henrik Nordström:
>
>      http://lists.phcomp.co.uk/pipermail/arm-netbook/2012-June/004341.html
>
> Because the BROM code is using some parts of the SRAM for itself, only a
> few areas are available for use in u-boot. Currently the SPL is loaded
> into the "0x2000-0x5cff Free for program use" area and the stack pointer
> is at the end of this area. This is barely enough to fit just the current
> SPL and leaves almost no headroom for the future code.
>
> This patch enables the use of a more compact Thumb2 mode for compiling the
> FEL SPL binary. And also relocates the stack to another "0x8000-0xbfff Free
> for program use" area. Additionally, the BSS segment is cleared.
>
> Signed-off-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>

Looks good:

Acked-by: Hans de Goede <hdegoede at redhat.com>

Regards,

Hans

> ---
>   arch/arm/cpu/armv7/sunxi/Makefile           |  1 +
>   arch/arm/cpu/armv7/sunxi/start_fel.S        | 42 +++++++++++++++++++++++++++++
>   arch/arm/cpu/armv7/sunxi/u-boot-spl-fel.lds |  4 +--
>   include/configs/sunxi-common.h              |  2 --
>   4 files changed, 45 insertions(+), 4 deletions(-)
>   create mode 100644 arch/arm/cpu/armv7/sunxi/start_fel.S
>
> diff --git a/arch/arm/cpu/armv7/sunxi/Makefile b/arch/arm/cpu/armv7/sunxi/Makefile
> index a64bfa1..b3eff98 100644
> --- a/arch/arm/cpu/armv7/sunxi/Makefile
> +++ b/arch/arm/cpu/armv7/sunxi/Makefile
> @@ -21,5 +21,6 @@ ifdef CONFIG_SPL_BUILD
>   obj-$(CONFIG_SUN7I)	+= dram.o
>   ifdef CONFIG_SPL_FEL
>   obj-y	+= start.o
> +extra-y += start_fel.o
>   endif
>   endif
> diff --git a/arch/arm/cpu/armv7/sunxi/start_fel.S b/arch/arm/cpu/armv7/sunxi/start_fel.S
> new file mode 100644
> index 0000000..2789fd9
> --- /dev/null
> +++ b/arch/arm/cpu/armv7/sunxi/start_fel.S
> @@ -0,0 +1,42 @@
> +/*
> + * Copyright (c) 2014 Siarhei Siamashka <siarhei.siamashka at gmail.com>
> + *
> + * SPDX-License-Identifier:	GPL-2.0+
> + */
> +
> +.syntax unified
> +.text
> +.arm
> +.arch armv7a
> +.p2align 2
> +
> +.globl _start_fel
> +.globl s_init
> +.globl __bss_start
> +.globl __bss_end
> +
> +_start_fel:
> +	/* Relocate stack to the 0x8000-0xBFFF area */
> +	mov	r0, #0xC000
> +	str	sp, [r0, #-4]!
> +	str	lr, [r0, #-4]!
> +	adr	lr, _exit_fel /* Return back to '_exit_fel' */
> +	mov	sp, r0
> +
> +	/* Erase the BSS segment */
> +	ldr	r0, =__bss_start
> +	ldr	r1, =__bss_end
> +	mov	r2, #0
> +0:	cmp	r0, r1
> +	strbne	r2, [r0], #1
> +	bne	0b
> +
> +	/* Pass control to the 's_init()' function */
> +	b	s_init
> +
> +_exit_fel:
> +	/* Relocate stack back and return */
> +	mov	r0, #0xC000
> +	ldr	sp, [r0, #-4]!
> +	ldr	lr, [r0, #-4]!
> +	bx	lr
> diff --git a/arch/arm/cpu/armv7/sunxi/u-boot-spl-fel.lds b/arch/arm/cpu/armv7/sunxi/u-boot-spl-fel.lds
> index 364e35c..418c2fc 100644
> --- a/arch/arm/cpu/armv7/sunxi/u-boot-spl-fel.lds
> +++ b/arch/arm/cpu/armv7/sunxi/u-boot-spl-fel.lds
> @@ -6,7 +6,7 @@
>    */
>   OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
>   OUTPUT_ARCH(arm)
> -ENTRY(s_init)
> +ENTRY(_start_fel)
>   SECTIONS
>   {
>   	. = 0x00002000;
> @@ -14,7 +14,7 @@ SECTIONS
>   	. = ALIGN(4);
>   	.text :
>   	{
> -		*(.text.s_init)
> +		arch/arm/cpu/armv7/sunxi/start_fel.o	(.text)
>   		*(.text*)
>   	}
>
> diff --git a/include/configs/sunxi-common.h b/include/configs/sunxi-common.h
> index 5d72d62..4b980e9 100644
> --- a/include/configs/sunxi-common.h
> +++ b/include/configs/sunxi-common.h
> @@ -18,10 +18,8 @@
>    */
>   #define CONFIG_SUNXI		/* sunxi family */
>   #ifdef CONFIG_SPL_BUILD
> -#ifndef CONFIG_SPL_FEL
>   #define CONFIG_SYS_THUMB_BUILD	/* Thumbs mode to save space in SPL */
>   #endif
> -#endif
>
>   #include <asm/arch/cpu.h>	/* get chip and board defs */
>
>