Re: [PATCH] powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline

Nicholas Piggin
2017-08-31T12:08:19Z

On Thu, 31 Aug 2017 17:17:41 +0530
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> wrote:

> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
>
> commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via
> stop-api only on Hotplug") clears the PECE1 bit of the LPCR via
> stop-api during CPU-Hotplug to prevent wakeup due to a decrementer on
> an offlined CPU which is in a deep stop state.
>
> In the case where the stop-api support is found to be lacking, the
> commit 785a12afdb4a ("powerpc/powernv/idle: Disable LOSE_FULL_CONTEXT
> states when stop-api fails") disables deep states that lose hypervisor
> context. Thus in this case, the offlined CPU will be put to some
> shallow idle state.
>
> However, we currently unconditionally clear the PECE1 in LPCR via
> stop-api during CPU-Hotplug even when deep states are disabled due to
> stop-api failure.
>
> Fix this by clearing PECE1 of LPCR via stop-api during CPU-Hotplug
> *only* when the offlined CPU will be put to a deep state that loses
> hypervisor context.

This looks okay to me. The bug is due to calling opal_slw_set_reg when
firmware has not enabled that feature, right?

>
> Fixes: commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via
> stop-api only on Hotplug")
>
> Reported-by: Pavithra Prakash <pavirampu@linux.vnet.ibm.com>
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> ---
> arch/powerpc/platforms/powernv/idle.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 9f59041..23f8fba 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -393,7 +393,13 @@ static void pnv_program_cpu_hotplug_lpcr(unsigned int cpu, u64 lpcr_val)
> u64 pir = get_hard_smp_processor_id(cpu);
>
> mtspr(SPRN_LPCR, lpcr_val);
> - opal_slw_set_reg(pir, SPRN_LPCR, lpcr_val);
> +
> + /*
> + * Program the LPCR via stop-api only for deepest stop state
> + * can lose hypervisor context.
> + */
> + if (supported_cpuidle_states & OPAL_PM_LOSE_FULL_CONTEXT)
> + opal_slw_set_reg(pir, SPRN_LPCR, lpcr_val);
> }
>
> /*