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

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