[U-Boot] [PATCH v5 2/7] arm: relocation: clear .bss section with arch memset if defined

[Lukasz Majewski]

Hi Przemyslaw,

> For ARM architecture, enable the CONFIG_USE_ARCH_MEMSET/MEMCPY,
> will highly increase the memset/memcpy performance. This is able
> thanks to the ARM multiple register instructions.
> 
> Unfortunatelly the relocation is done without the cache enabled,
> so it takes some time, but zeroing the BSS memory takes much more
> longer, especially for the configs with big static buffers.
> 
> A quick test confirms, that the boot time improvement after using
> the arch memcpy for relocation has no significant meaning.
> The same test confirms that enable the memset for zeroing BSS,
> reduces the boot time.
> 
> So this patch enables the arch memset for zeroing the BSS after
> the relocation process. For ARM boards, this can be enabled
> in board configs by defining: 'CONFIG_USE_ARCH_MEMSET'.
> 
> This was tested on Trats2.
> A quick test with trace. Boot time from start to main_loop() entry:
> - ~1384ms - before this change
> -  ~888ms - after this change
> 
> Signed-off-by: Przemyslaw Marczak <p.marczak at samsung.com>
> Reviewed-by: Simon Glass <sjg at chromium.org>
> Cc: Albert Aribaud <albert.u.boot at aribaud.net>
> Cc: Tom Rini <trini at ti.com>
> ---
> Changes V3, V4, V5
> - none
> ---
>  arch/arm/lib/crt0.S | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
> index 22df3e5..fab3d2c 100644
> --- a/arch/arm/lib/crt0.S
> +++ b/arch/arm/lib/crt0.S
> @@ -115,14 +115,22 @@ here:
>  	bl	c_runtime_cpu_setup	/* we still call old
> routine here */ 
>  	ldr	r0, =__bss_start	/* this is
> auto-relocated! */
> -	ldr	r1, =__bss_end		/* this is
> auto-relocated! */ 
> +#ifdef CONFIG_USE_ARCH_MEMSET
> +	ldr	r3, =__bss_end		/* this is
> auto-relocated! */
> +	mov	r1, #0x00000000		/* prepare zero to
> clear BSS */ +
> +	subs	r2, r3, r0		/* r2 = memset len */
> +	bl	memset
> +#else
> +	ldr	r1, =__bss_end		/* this is
> auto-relocated! */ mov	r2, #0x00000000		/*
> prepare zero to clear BSS */ 
>  clbss_l:cmp	r0, r1			/* while not at end
> of BSS */ strlo	r2, [r0]		/* clear 32-bit BSS
> word */ addlo	r0, r0, #4		/* move to next */
>  	blo	clbss_l
> +#endif
>  
>  	bl coloured_LED_init
>  	bl red_led_on

Acked-by: Lukasz Majewski <l.majewski at samsung.com>

-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group