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

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Message-ID: <ab13c87c800fe03d5045ae3fb7442a7f050be9ba.camel@linux.intel.com>
Date: Sat, 12 Oct 2024 17:40:11 -0700
From: srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To: "David E. Box" <david.e.box@...ux.intel.com>, hdegoede@...hat.com, 
	ilpo.jarvinen@...ux.intel.com, rjw@...ysocki.net, 
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org
Cc: ricardo.neri-calderon@...ux.intel.com
Subject: Re: [PATCH V2 2/2] platform/x86/intel/pmc: Disable C1 auto-demotion
 during suspend

+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@...ux.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);