Re: [PATCH] PCI/PM: Do not generate wakeup event when runtime resuming bus

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Thursday, October 29, 2020 10:24:53 AM CET Mika Westerberg wrote:
> When a PCI bridge is runtime resumed from D3cold the underlying bus is
> walked and the attached devices are runtime resumed as well. However, in
> addition to that we also generate a wakeup event for these devices even
> though this actually is not a real wakeup event coming from the
> hardware.
> 
> Normally this does not cause problems but when combined with
> /sys/power/wakeup_count like using the steps below:
> 
>   # count=$(cat /sys/power/wakeup_count)
>   # echo $count > /sys/power/wakeup_count
>   # echo mem > /sys/power/state
> 
> The system suspend cycle might get aborted at this point if a PCI bridge
> that was runtime suspended (D3cold) was runtime resumed for any reason.
> The runtime resume calls pci_wakeup_bus() and that generates wakeup
> event increasing wakeup_count.
> 
> Since this is not a real wakeup event we can prevent the above from
> happening by removing the call to pci_wakeup_event() in
> pci_wakeup_bus(). While there rename pci_wakeup_bus() to
> pci_resume_bus() to better reflect what it does.
> 
> Reported-by: Utkarsh Patel <utkarsh.h.patel@intel.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
>  drivers/gpu/vga/vga_switcheroo.c |  2 +-
>  drivers/pci/pci.c                | 16 +++++-----------
>  include/linux/pci.h              |  2 +-
>  3 files changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
> index 087304b1a5d7..8843b078ad4e 100644
> --- a/drivers/gpu/vga/vga_switcheroo.c
> +++ b/drivers/gpu/vga/vga_switcheroo.c
> @@ -1039,7 +1039,7 @@ static int vga_switcheroo_runtime_resume(struct device *dev)
>  	mutex_lock(&vgasr_mutex);
>  	vga_switcheroo_power_switch(pdev, VGA_SWITCHEROO_ON);
>  	mutex_unlock(&vgasr_mutex);
> -	pci_wakeup_bus(pdev->bus);
> +	pci_resume_bus(pdev->bus);
>  	ret = dev->bus->pm->runtime_resume(dev);
>  	if (ret)
>  		return ret;
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 6d4d5a2f923d..b25dfa63eeb9 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1174,26 +1174,20 @@ int pci_platform_power_transition(struct pci_dev *dev, pci_power_t state)
>  }
>  EXPORT_SYMBOL_GPL(pci_platform_power_transition);
>  
> -/**
> - * pci_wakeup - Wake up a PCI device
> - * @pci_dev: Device to handle.
> - * @ign: ignored parameter
> - */
> -static int pci_wakeup(struct pci_dev *pci_dev, void *ign)
> +static int pci_resume_one(struct pci_dev *pci_dev, void *ign)
>  {
> -	pci_wakeup_event(pci_dev);
>  	pm_request_resume(&pci_dev->dev);
>  	return 0;
>  }
>  
>  /**
> - * pci_wakeup_bus - Walk given bus and wake up devices on it
> + * pci_resume_bus - Walk given bus and runtime resume devices on it
>   * @bus: Top bus of the subtree to walk.
>   */
> -void pci_wakeup_bus(struct pci_bus *bus)
> +void pci_resume_bus(struct pci_bus *bus)
>  {
>  	if (bus)
> -		pci_walk_bus(bus, pci_wakeup, NULL);
> +		pci_walk_bus(bus, pci_resume_one, NULL);
>  }
>  
>  static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
> @@ -1256,7 +1250,7 @@ int pci_power_up(struct pci_dev *dev)
>  		 * may be powered on into D0uninitialized state, resume them to
>  		 * give them a chance to suspend again
>  		 */
> -		pci_wakeup_bus(dev->subordinate);
> +		pci_resume_bus(dev->subordinate);
>  	}
>  
>  	return pci_raw_set_power_state(dev, PCI_D0);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 22207a79762c..9256ef2e4327 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1271,7 +1271,7 @@ bool pci_dev_run_wake(struct pci_dev *dev);
>  void pci_d3cold_enable(struct pci_dev *dev);
>  void pci_d3cold_disable(struct pci_dev *dev);
>  bool pcie_relaxed_ordering_enabled(struct pci_dev *dev);
> -void pci_wakeup_bus(struct pci_bus *bus);
> +void pci_resume_bus(struct pci_bus *bus);
>  void pci_bus_set_current_state(struct pci_bus *bus, pci_power_t state);
>  
>  /* For use by arch with custom probe code */
>