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

[David E. Box]

On Thu, 2024-10-10 at 19:09 -0700, srinivas pandruvada wrote:
> 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@xxxxxxxxxxxxxxx>
> > ---
> > 
> > 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?

Thought it could be useful but it can be removed.

> 
> > +}
> > +
> > +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?

To ensure that the cpu doesn't change between the next two calls.

David

> 
> 
> 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);
>