[PATCH] powerpc/xics: Adjust interrupt receive priority for offline cpus

[Michael Neuling]

On Thu, 2017-02-23 at 16:24 +0530, Vaidyanathan Srinivasan wrote:
> Offline CPUs need to receive IPIs through XIVE when they are
> in stop state and wakeup from that state.
> 
> Reduce interrupt receive priority in order to receive XIVE
> wakeup interrupts when in offline state.
> 
> LOWEST_PRIORITY would allow all interrupts to be delivered
> as wakeup events.

This needs to be expanded to explain why "DEFAULT" doesn't work in this case.

This also needs an explicit statement that "It fixes onlining of CPUs on
POWER9".  I'd even advocate for making that the patch subject. 

Also if it's the right fix, it needs a cc:stable.

Mikey


> Signed-off-by: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>
> ---
>  arch/powerpc/sysdev/xics/xics-common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/sysdev/xics/xics-common.c
> b/arch/powerpc/sysdev/xics/xics-common.c
> index 69d858e..c674a9d 100644
> --- a/arch/powerpc/sysdev/xics/xics-common.c
> +++ b/arch/powerpc/sysdev/xics/xics-common.c
> @@ -199,7 +199,7 @@ void xics_migrate_irqs_away(void)
>  	xics_set_cpu_giq(xics_default_distrib_server, 0);
>  
>  	/* Allow IPIs again... */
> -	icp_ops->set_priority(DEFAULT_PRIORITY);
> +	icp_ops->set_priority(LOWEST_PRIORITY);
>  
>  	for_each_irq_desc(virq, desc) {
>  		struct irq_chip *chip;