Message-ID: <20190605113635.GD84290@google.com>
Date:   Wed, 5 Jun 2019 06:36:35 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: PM: Avoid resuming devices in D3hot during system
 suspend

On Mon, Jun 03, 2019 at 12:10:28PM +0200, Rafael J. Wysocki wrote:
> On Friday, May 31, 2019 11:16:48 PM CEST Bjorn Helgaas wrote:
> > On Fri, May 31, 2019 at 11:49:30AM +0200, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > 
> > > The current code resumes devices in D3hot during system suspend if
> > > the target power state for them is D3cold, but that is not necessary
> > > in general.  It only is necessary to do that if the platform firmware
> > > requires the device to be resumed, but that should be covered by
> > > the platform_pci_need_resume() check anyway, so rework
> > > pci_dev_keep_suspended() to avoid returning 'false' for devices
> > > in D3hot which need not be resumed due to platform firmware
> > > requirements.
> > > 
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > ---
> > >  drivers/pci/pci.c |   15 ++++++++++++---
> > >  1 file changed, 12 insertions(+), 3 deletions(-)
> > > 
> > > Index: linux-pm/drivers/pci/pci.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/pci/pci.c
> > > +++ linux-pm/drivers/pci/pci.c
> > > @@ -2474,10 +2474,19 @@ bool pci_dev_keep_suspended(struct pci_d
> > >  {
> > >  	struct device *dev = &pci_dev->dev;
> > >  	bool wakeup = device_may_wakeup(dev);
> > > +	pci_power_t target_state;
> > >  
> > > -	if (!pm_runtime_suspended(dev)
> > > -	    || pci_target_state(pci_dev, wakeup) != pci_dev->current_state
> > > -	    || platform_pci_need_resume(pci_dev))
> > > +	if (!pm_runtime_suspended(dev) || platform_pci_need_resume(pci_dev))
> > > +		return false;
> > > +
> > > +	target_state = pci_target_state(pci_dev, wakeup);
> > 
> > Nit, add a blank line here.
> 
> OK
> 
> > > +	/*
> > > +	 * If the earlier platform check has not triggered, D3cold is just power
> > > +	 * removal on top of D3hot, so no need to resume the device in that
> > > +	 * case.
> > > +	 */
> > > +	if (target_state != pci_dev->current_state &&
> > > +	    target_state != PCI_D3cold && pci_dev->current_state != PCI_D3hot)
> > >  		return false;
> > 
> > This is more a comment on the existing code than on this particular
> > patch, but I find this whole function hard to understand, and I think
> > one reason is that there are a lot of negative conditions, both in
> > this function and in its callers.  This "target_state != ... &&
> > target_state != ...  && current_state != ..." is one example.  Another
> > is the function name itself.  It might be easier to read as something
> > like this:
> > 
> >   bool pci_dev_need_resume(...)
> >   {
> >     if (!pm_runtime_suspended(...))
> >       return true;
> > 
> >     if (platform_pci_need_resume(...))
> >       return true;
> > 
> >     if (target_state != current_state)
> >       return true;
> 
> Please see the appended (untested) patch on top of the $subject one.

I like it a lot, thanks!  I think it makes it a lot more readable.

> > Another reason I think it's hard to read is that
> > "pci_dev_keep_suspended" suggests that this is a pure boolean function
> > without side-effects, but in fact it also fiddles with the PME state
> > in some cases.  I don't have any ideas for that part.
> 
> Well, I can only propose to put the PME adjustment part into a separate function like
> in the patch below.
> 
> ---
>  drivers/pci/pci-driver.c |   21 ++++++++++++++++---
>  drivers/pci/pci.c        |   50 ++++++++++++++++++++++++-----------------------
>  drivers/pci/pci.h        |    3 +-
>  3 files changed, 46 insertions(+), 28 deletions(-)
> 
> Index: linux-pm/drivers/pci/pci.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci.c
> +++ linux-pm/drivers/pci/pci.c
> @@ -2459,54 +2459,56 @@ bool pci_dev_run_wake(struct pci_dev *de
>  EXPORT_SYMBOL_GPL(pci_dev_run_wake);
>  
>  /**
> - * pci_dev_keep_suspended - Check if the device can stay in the suspended state.
> + * pci_dev_need_resume - Check if the device can stay in the suspended state.
>   * @pci_dev: Device to check.
>   *
> - * Return 'true' if the device is runtime-suspended, it doesn't have to be
> + * Return 'false' if the device is runtime-suspended, it doesn't have to be
>   * reconfigured due to wakeup settings difference between system and runtime
>   * suspend and the current power state of it is suitable for the upcoming
>   * (system) transition.
> - *
> - * If the device is not configured for system wakeup, disable PME for it before
> - * returning 'true' to prevent it from waking up the system unnecessarily.
>   */
> -bool pci_dev_keep_suspended(struct pci_dev *pci_dev)
> +bool pci_dev_need_resume(struct pci_dev *pci_dev)
>  {
>  	struct device *dev = &pci_dev->dev;
> -	bool wakeup = device_may_wakeup(dev);
>  	pci_power_t target_state;
>  
>  	if (!pm_runtime_suspended(dev) || platform_pci_need_resume(pci_dev))
> -		return false;
> +		return true;
>  
> -	target_state = pci_target_state(pci_dev, wakeup);
> +	target_state = pci_target_state(pci_dev, device_may_wakeup(dev));
>  	/*
>  	 * If the earlier platform check has not triggered, D3cold is just power
>  	 * removal on top of D3hot, so no need to resume the device in that
>  	 * case.
>  	 */
> -	if (target_state != pci_dev->current_state &&
> -	    target_state != PCI_D3cold && pci_dev->current_state != PCI_D3hot)
> -		return false;
> +	return target_state != pci_dev->current_state &&
> +		target_state != PCI_D3cold &&
> +		pci_dev->current_state != PCI_D3hot;
> +}
> +
> +/**
> + * pci_dev_adjust_pme - Adjust PME setting for a suspended device.
> + * @pci_dev: Device to check.
> + *
> + * If the device is not configured for system wakeup, disable PME for it to
> + * prevent it from waking up the system unnecessarily.
> + */
> +void pci_dev_adjust_pme(struct pci_dev *pci_dev)
> +{
> +	struct device *dev = &pci_dev->dev;
>  
> -	/*
> -	 * At this point the device is good to go unless it's been configured
> -	 * to generate PME at the runtime suspend time, but it is not supposed
> -	 * to wake up the system.  In that case, simply disable PME for it
> -	 * (it will have to be re-enabled on exit from system resume).
> -	 *
> -	 * If the device's power state is D3cold and the platform check above
> -	 * hasn't triggered, the device's configuration is suitable and we don't
> -	 * need to manipulate it at all.
> -	 */
>  	spin_lock_irq(&dev->power.lock);
>  
> +	/*
> +	 * If the device's power state is D3cold and the platform check in
> +	 * pci_dev_need_resume() hasn't triggered, the device's configuration is
> +	 * suitable and it need not be touched.

I guess "it need not be touched" == "we don't need to disable PME"?

> +	 */
>  	if (pm_runtime_suspended(dev) && pci_dev->current_state < PCI_D3cold &&
> -	    !wakeup)
> +	    !device_may_wakeup(dev))
>  		__pci_pme_active(pci_dev, false);
>  
>  	spin_unlock_irq(&dev->power.lock);
> -	return true;
>  }
>  
>  /**
> Index: linux-pm/drivers/pci/pci-driver.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-driver.c
> +++ linux-pm/drivers/pci/pci-driver.c
> @@ -679,6 +679,7 @@ static bool pci_has_legacy_pm_support(st
>  static int pci_pm_prepare(struct device *dev)
>  {
>  	struct device_driver *drv = dev->driver;
> +	struct pci_dev *pci_dev = to_pci_dev(dev);
>  
>  	if (drv && drv->pm && drv->pm->prepare) {
>  		int error = drv->pm->prepare(dev);
> @@ -688,7 +689,15 @@ static int pci_pm_prepare(struct device
>  		if (!error && dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_PREPARE))
>  			return 0;
>  	}
> -	return pci_dev_keep_suspended(to_pci_dev(dev));
> +	if (pci_dev_need_resume(pci_dev))
> +		return 0;
> +
> +	/*
> +	 * The PME setting needs to be adjusted here in case the direct-complete
> +	 * optimization is used with respect to this device.
> +	 */
> +	pci_dev_adjust_pme(pci_dev);
> +	return 1;
>  }
>  
>  static void pci_pm_complete(struct device *dev)
> @@ -758,9 +767,11 @@ static int pci_pm_suspend(struct device
>  	 * better to resume the device from runtime suspend here.
>  	 */
>  	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) ||
> -	    !pci_dev_keep_suspended(pci_dev)) {
> +	    pci_dev_need_resume(pci_dev)) {
>  		pm_runtime_resume(dev);
>  		pci_dev->state_saved = false;
> +	} else {
> +		pci_dev_adjust_pme(pci_dev);
>  	}
>  
>  	if (pm->suspend) {
> @@ -1108,8 +1119,12 @@ static int pci_pm_poweroff(struct device
>  
>  	/* The reason to do that is the same as in pci_pm_suspend(). */
>  	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) ||
> -	    !pci_dev_keep_suspended(pci_dev))
> +	    pci_dev_need_resume(pci_dev)) {
>  		pm_runtime_resume(dev);
> +		pci_dev->state_saved = false;
> +	} else {
> +		pci_dev_adjust_pme(pci_dev);
> +	}
>  
>  	pci_dev->state_saved = false;
>  	if (pm->poweroff) {
> Index: linux-pm/drivers/pci/pci.h
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci.h
> +++ linux-pm/drivers/pci/pci.h
> @@ -82,7 +82,8 @@ int pci_finish_runtime_suspend(struct pc
>  void pcie_clear_root_pme_status(struct pci_dev *dev);
>  int __pci_pme_wakeup(struct pci_dev *dev, void *ign);
>  void pci_pme_restore(struct pci_dev *dev);
> -bool pci_dev_keep_suspended(struct pci_dev *dev);
> +bool pci_dev_need_resume(struct pci_dev *dev);
> +void pci_dev_adjust_pme(struct pci_dev *dev);
>  void pci_dev_complete_resume(struct pci_dev *pci_dev);
>  void pci_config_pm_runtime_get(struct pci_dev *dev);
>  void pci_config_pm_runtime_put(struct pci_dev *dev);
> 
> 
> 

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