[PATCH 18/18] powerpc/64s: move power4 idle entirely to C

[Christophe Leroy]

Le 05/11/2020 à 15:34, Nicholas Piggin a écrit :
> Christophe asked about doing this, most of the code is still in
> asm but maybe it's slightly nicer? I don't know if it's worthwhile.

Heu... I don't think I was asking for that, but why not, see later comments.

At first I was just asking to write the following in C:

+
+	.globl power4_idle_nap_return
+power4_idle_nap_return:
+	blr


In extenso, instead of the above do somewhere something like:

void power4_idle_nap_return(void)
{
}


> ---
>   arch/powerpc/kernel/idle.c        | 25 ++++++++++++++++++++-----
>   arch/powerpc/kernel/idle_book3s.S | 22 ----------------------
>   2 files changed, 20 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
> index ae0e2632393d..849e77a45915 100644
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -72,6 +72,9 @@ int powersave_nap;
>   #ifdef CONFIG_PPC_970_NAP
>   void power4_idle(void)
>   {
> +	unsigned long msr_idle = MSR_KERNEL|MSR_EE|MSR_POW;
> +	unsigned long tmp1, tmp2;
> +
>   	if (!cpu_has_feature(CPU_FTR_CAN_NAP))
>   		return;
>   
> @@ -84,13 +87,25 @@ void power4_idle(void)
>   	if (cpu_has_feature(CPU_FTR_ALTIVEC))
>   		asm volatile("DSSALL ; sync" ::: "memory");
>   
> -	power4_idle_nap();
> -
> +	asm volatile(
> +"	ld	%0,PACA_THREAD_INFO(r13)		\n"
> +"	ld	%1,TI_LOCAL_FLAGS(%0)			\n"
> +"	ori	%1,%1,_TLF_NAPPING			\n"
> +"	std	%1,TI_LOCAL_FLAGS(%0)			\n"

Can't this just be:

	current_thread_info()->local_flags |= _TLF_NAPPING;

>   	/*
> -	 * power4_idle_nap returns with interrupts enabled (soft and hard).
> -	 * to our caller with interrupts enabled (soft and hard). Our caller
> -	 * can cope with either interrupts disabled or enabled upon return.
> +	 * NAPPING bit is set, from this point onward nap_adjust_return()
> +	 * will cause interrupts to return to power4_idle_nap_return.
>   	 */
> +"1:	sync						\n"
> +"	isync						\n"
> +"	mtmsrd	%2					\n"
> +"	isync						\n"
> +"	b	1b					\n"

And this:

	for (;;) {
		mb();
		isync();
		mtmsr(MSR_KERNEL|MSR_EE|MSR_POW);
		isync();
	}


> +"	.globl power4_idle_nap_return			\n"
> +"power4_idle_nap_return:				\n"
> +	: "=r"(tmp1), "=r"(tmp2)
> +	: "r"(msr_idle)
> +	);
>   }
>   #endif
>   

Christophe