Re: [PATCH V2 2/2] platform/x86/intel/pmc: Disable C1 auto-demotion during suspend

srinivas pandruvada
2024-10-13T00:40:14Z

+Ricardo

On Thu, 2024-10-10 at 17:36 -0700, David E. Box wrote:
> On some platforms, aggressive C1 auto-demotion may lead to failure to
> enter
> the deepest C-state during suspend-to-idle, causing high power
> consumption.
> To prevent this, disable C1 auto-demotion during suspend and re-
> enable on
> resume.
>
> Signed-off-by: David E. Box <david.e.box@linux.intel.com>
> ---
>

[...]

>  void cnl_suspend(struct pmc_dev *pmcdev)
>  {
> + if (!pm_suspend_via_firmware()) {
> + preempt_disable();
> + disable_c1_auto_demote(NULL);
> + smp_call_function(disable_c1_auto_demote, NULL, 0);
> + preempt_enable();
> + }
>
As suggested by Ricardo using the following will work avoiding separate
local CPU call. Preemption will be disabled, no need separate call.
Also cpu_online_mask can't be changed during these callbacks.

if (!pm_suspend_via_firmware())
on_each_cpu(disable_c1_auto_demote, NULL, true);

I think you need wait=true. I have seen on some occasions you will miss
msr write as we called mwait before before async calls finished.

Thanks,
Srinivas

> +
>   /*
>   * Due to a hardware limitation, the GBE LTR blocks PC10
>   * when a cable is attached. To unblock PC10 during suspend,
> @@ -218,6 +264,13 @@ void cnl_suspend(struct pmc_dev *pmcdev)
>
>  int cnl_resume(struct pmc_dev *pmcdev)
>  {
> + if (!pm_suspend_via_firmware()) {
> + preempt_disable();
> + restore_c1_auto_demote(NULL);
> + smp_call_function(restore_c1_auto_demote, NULL, 0);
> + preempt_enable();
> + }
> +
>   pmc_core_send_ltr_ignore(pmcdev, 3, 0);
>
>   return pmc_core_resume_common(pmcdev);