Re: [PATCH] PCI / ACPI / PM: Resume all bridges on suspend-to-RAM

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Aug 16, 2018 at 12:56:46PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Commit 26112ddc254c (PCI / ACPI / PM: Resume bridges w/o drivers on
> suspend-to-RAM) attempted to fix a functional regression resulting
> from commit c62ec4610c40 (PM / core: Fix direct_complete handling
> for devices with no callbacks) by resuming PCI bridges without
> drivers (that is, "parallel PCI" ones) during system-wide suspend if
> the target system state is not ACPI S0 (working state).
> 
> That turns out insufficient, however, as it is reported that, at
> least in one case, the platform firmware gets confused if a PCIe
> root port is suspended before entering the ACPI S3 sleep state.
> 
> For this reason, drop the driver check from acpi_pci_need_resume()
> and resume all bridges (including PCIe ports with drivers) during
> system-wide suspend if the target system state is not ACPI S0.
> 
> [If the target system state is ACPI S0, it means suspend-to-idle
>  and the platform firmware is not going to be invoked to actually
>  suspend the system, so there is no need to resume the bridges in
>  that case.]
> 
> Fixes: c62ec4610c40 (PM / core: Fix direct_complete handling for devices with no callbacks)
> Reported-by: teika kazura <teika@gmx.com>
> Tested-by: teika kazura <teika@gmx.com>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200675
> Cc: 4.15+ <stable@vger.kernel.org> # 4.15+: 26112ddc254c (PCI / ACPI / PM: Resume bridges ...)
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

Thanks for doing this.  I don't like dependencies on the PCIe
PM/AER/hotplug/etc features being implemented as a "driver" because
they could be implemented in the PCI core directly.

> ---
>  drivers/pci/pci-acpi.c |    6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -632,13 +632,11 @@ static bool acpi_pci_need_resume(struct
>  	/*
>  	 * In some cases (eg. Samsung 305V4A) leaving a bridge in suspend over
>  	 * system-wide suspend/resume confuses the platform firmware, so avoid
> -	 * doing that, unless the bridge has a driver that should take care of
> -	 * the PM handling.  According to Section 16.1.6 of ACPI 6.2, endpoint
> +	 * doing that.  According to Section 16.1.6 of ACPI 6.2, endpoint
>  	 * devices are expected to be in D3 before invoking the S3 entry path
>  	 * from the firmware, so they should not be affected by this issue.
>  	 */
> -	if (pci_is_bridge(dev) && !dev->driver &&
> -	    acpi_target_system_state() != ACPI_STATE_S0)
> +	if (pci_is_bridge(dev) && acpi_target_system_state() != ACPI_STATE_S0)
>  		return true;
>  
>  	if (!adev || !acpi_device_power_manageable(adev))
>