[PATCH 02/16] mips: add support to restore exception vector base before booting linux

[Daniel Schwierzeck]

Am 08.01.20 um 04:00 schrieb Weijie Gao:
> In U-Boot the exception vector base will be moved to top of memory, to be
> used to display register dump when exception occurs.
> 
> But some old linux kernel does not honor the base set in CP0_EBASE. A
> modified exception vector base will cause kernel crash.
> 
> This patch adds an option to enable reset exception vector base to
> 0x80000000 before booting linux kernel.
> 
> Signed-off-by: Weijie Gao <weijie.gao at mediatek.com>
> ---
>  arch/mips/Kconfig     | 13 +++++++++++++
>  arch/mips/lib/bootm.c |  9 +++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index a3ae603044..4688717593 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -287,6 +287,19 @@ config MIPS_RELOCATION_TABLE_SIZE
>  
>  	  If unsure, leave at the default value.
>  
> +config RESTORE_EXCEPTION_VECTOR_BASE
> +	bool "Restore exception vector base before booting linux kernel"
> +	default n
> +	help
> +	  In U-Boot the exception vector base will be moved to top of memory,
> +	  to be used to display register dump when exception occurs.
> +	  But some old linux kernel does not honor the base set in CP0_EBASE.
> +	  A modified exception vector base will cause kernel crash.
> +
> +	  This option will set exception vector base to 0x80000000.

Does it make sense to make the base address configurable and let it
default to 0x80000000?

> +
> +	  If unsure, say N.
> +
>  endmenu
>  
>  menu "OS boot interface"
> diff --git a/arch/mips/lib/bootm.c b/arch/mips/lib/bootm.c
> index 8c0d7672f2..86ea082fd0 100644
> --- a/arch/mips/lib/bootm.c
> +++ b/arch/mips/lib/bootm.c
> @@ -294,6 +294,15 @@ static void boot_jump_linux(bootm_headers_t *images)
>  	bootstage_report();
>  #endif
>  
> +#ifdef CONFIG_RESTORE_EXCEPTION_VECTOR_BASE
> +	/* Restore EBASE for compatibility */
> +	set_c0_status(ST0_BEV);
> +	execution_hazard_barrier();
> +	write_c0_ebase(KSEG0);
> +	clear_c0_status(ST0_BEV);
> +	execution_hazard_barrier();
> +#endif
> +

could you move this to a function trap_restore() in arch/mips/lib/traps.c?

Also prefer the following over #ifdef:

    if (CONFIG_IS_ENABLED(RESTORE_EXCEPTION_VECTOR_BASE))
        trap_restore();

Alternatively you could simply define trap_restore() as empty static
inline function if RESTORE_EXCEPTION_VECTOR_BASE is disabled.

>  	if (images->ft_len)
>  		kernel(-2, (ulong)images->ft_addr, 0, 0);
>  	else
> 

-- 
- Daniel