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

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Message-ID: <c4513e7857b15ec9146a7b75d00e99987787ced4.camel@linux.intel.com>
Date: Thu, 10 Oct 2024 19:09:10 -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
Subject: Re: [PATCH V2 2/2] platform/x86/intel/pmc: Disable C1 auto-demotion
 during suspend

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>
> ---
> 
> V2 - Remove #define DEBUG
>    - Move refactor of cnl_resume() to separate patch
>    - Use smp_call_function() to disable and restore C1_AUTO_DEMOTE
>    - Add comment that the MSR is per core, not per package.
>    - Add comment that the online cpu mask remains unchanged during
>      suspend due to frozen userspace.
> 
>  drivers/platform/x86/intel/pmc/cnp.c | 53
> ++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/drivers/platform/x86/intel/pmc/cnp.c
> b/drivers/platform/x86/intel/pmc/cnp.c
> index 513c02670c5a..f12d4f0f9e93 100644
> --- a/drivers/platform/x86/intel/pmc/cnp.c
> +++ b/drivers/platform/x86/intel/pmc/cnp.c
> @@ -8,6 +8,8 @@
>   *
>   */
>  
> +#include <linux/smp.h>
> +#include <linux/suspend.h>
>  #include "core.h"
>  
>  /* Cannon Lake: PGD PFET Enable Ack Status Register(s) bitmap */
> @@ -206,8 +208,52 @@ const struct pmc_reg_map cnp_reg_map = {
>  	.etr3_offset = ETR3_OFFSET,
>  };
>  
> +
> +/*
> + * Disable C1 auto-demotion
> + *
> + * 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, we
> + * disable C1 auto-demotion during suspend and re-enable on resume.
> + *
> + * Note that, although MSR_PKG_CST_CONFIG_CONTROL has 'package' in
> its name, it
> + * is actually a per-core MSR on client platforms, affecting only a
> single CPU.
> + * Therefore, it must be configured on all online CPUs. The online
> cpu mask is
> + * unchanged during the phase of suspend/resume as user space is
> frozen.
> + */
> +
> +static DEFINE_PER_CPU(u64, pkg_cst_config);
> +
> +static void disable_c1_auto_demote(void *unused)
> +{
> +	int cpunum = smp_processor_id();
> +	u64 val;
> +
> +	rdmsrl(MSR_PKG_CST_CONFIG_CONTROL, val);
> +	per_cpu(pkg_cst_config, cpunum) = val;
> +	val &= ~NHM_C1_AUTO_DEMOTE;
> +	wrmsrl(MSR_PKG_CST_CONFIG_CONTROL, val);
> +	pr_debug("%s: cpu:%d cst %llx\n", __func__, cpunum, val);
Do you want to leave pr_debug?

> +}
> +
> +static void restore_c1_auto_demote(void *unused)
> +{
> +	int cpunum = smp_processor_id();
> +
> +	pr_debug("%s: cpu:%d cst %llx\n", __func__, cpunum,
> +		 per_cpu(pkg_cst_config, cpunum));
> +	wrmsrl(MSR_PKG_CST_CONFIG_CONTROL, per_cpu(pkg_cst_config,
> cpunum));
> +}
> +
>  void cnl_suspend(struct pmc_dev *pmcdev)
>  {
> +	if (!pm_suspend_via_firmware()) {
> +		preempt_disable();
Why do you need this?


Thanks,
Srinivas

> +		disable_c1_auto_demote(NULL);
> +		smp_call_function(disable_c1_auto_demote, NULL, 0);
> +		preempt_enable();
> +	}
> +
>  	/*
>  	 * 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);