[PATCH v2] generic: mips: support harts to boot from mips_warm_boot

[Samuel Holland]

Hi Chao-ying,

On 2025-07-22 6:04 PM, Chao-ying Fu wrote:
> We program reset base for harts (other than hart 0) to boot at
> mips_warm_boot that jumps to _start_warm. This helps to skip some code
> sequence to speed up.
> 
> Signed-off-by: Chao-ying Fu <cfu at mips.com>
> ---
>  platform/generic/mips/p8700.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/platform/generic/mips/p8700.c b/platform/generic/mips/p8700.c
> index 888a45c..8c93ebf 100644
> --- a/platform/generic/mips/p8700.c
> +++ b/platform/generic/mips/p8700.c
> @@ -140,6 +140,20 @@ static void power_up_other_cluster(u32 hartid)
>  }
>  #endif
>  
> +static void __attribute__((naked,no_instrument_function,aligned(4096)))

Please follow Jess's suggestion and use an assembly file like we already do for
platform/generic/andes/sleep.S. This will be more reliable than forever fighting
the compiler to keep it from inserting any instructions on its own. (Are you
_sure_ that this list of attributes covers every toolchain and configuration?)

Regards,
Samuel

> +mips_warm_boot(void)
> +{
> +  __asm__ __volatile__(
> +	"	j	_start_warm\n"
> +	"	.align	2\n"
> +	"	j	_start_warm\n"
> +	"	.align	2\n"
> +	"	j	_start_warm\n"
> +	"	.align	2\n"
> +	"	j	_start_warm\n"
> +	);
> +}
> +
>  static int mips_hart_start(u32 hartid, ulong saddr)
>  {
>  	unsigned int stat;
> @@ -150,6 +164,9 @@ static int mips_hart_start(u32 hartid, ulong saddr)
>  	if (hartid == 0)
>  		return SBI_ENOTSUPP;
>  
> +	/* Change reset base to mips_warm_boot */
> +	write_gcr_co_reset_base(hartid, (unsigned long)mips_warm_boot, local_p);
> +
>  	if (cpu_hart(hartid) == 0) {
>  		/* Ensure its coherency is disabled */
>  		write_gcr_co_coherence(hartid, 0, local_p);