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    Subject[PATCH 4.19 427/639] PCI: PM: Skip devices in D0 for suspend-to-idle
    Date
    From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

    [ Upstream commit 3e26c5feed2add218046ecf91bab3cfa9bf762a6 ]

    Commit d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
    attempted to avoid a problem with devices whose drivers want them to
    stay in D0 over suspend-to-idle and resume, but it did not go as far
    as it should with that.

    Namely, first of all, the power state of a PCI bridge with a
    downstream device in D0 must be D0 (based on the PCI PM spec r1.2,
    sec 6, table 6-1, if the bridge is not in D0, there can be no PCI
    transactions on its secondary bus), but that is not actively enforced
    during system-wide PM transitions, so use the skip_bus_pm flag
    introduced by commit d491f2b75237 for that.

    Second, the configuration of devices left in D0 (whatever the reason)
    during suspend-to-idle need not be changed and attempting to put them
    into D0 again by force is pointless, so explicitly avoid doing that.

    Fixes: d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
    Reported-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/pci/pci-driver.c | 47 ++++++++++++++++++++++++++++++----------
    1 file changed, 35 insertions(+), 12 deletions(-)

    diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
    index 5c9873fcbd08b..e69af9b8361dc 100644
    --- a/drivers/pci/pci-driver.c
    +++ b/drivers/pci/pci-driver.c
    @@ -526,7 +526,6 @@ static void pci_pm_default_resume_early(struct pci_dev *pci_dev)
    pci_power_up(pci_dev);
    pci_restore_state(pci_dev);
    pci_pme_restore(pci_dev);
    - pci_fixup_device(pci_fixup_resume_early, pci_dev);
    }

    /*
    @@ -833,18 +832,16 @@ static int pci_pm_suspend_noirq(struct device *dev)

    if (pci_dev->skip_bus_pm) {
    /*
    - * The function is running for the second time in a row without
    + * Either the device is a bridge with a child in D0 below it, or
    + * the function is running for the second time in a row without
    * going through full resume, which is possible only during
    - * suspend-to-idle in a spurious wakeup case. Moreover, the
    - * device was originally left in D0, so its power state should
    - * not be changed here and the device register values saved
    - * originally should be restored on resume again.
    + * suspend-to-idle in a spurious wakeup case. The device should
    + * be in D0 at this point, but if it is a bridge, it may be
    + * necessary to save its state.
    */
    - pci_dev->state_saved = true;
    - } else if (pci_dev->state_saved) {
    - if (pci_dev->current_state == PCI_D0)
    - pci_dev->skip_bus_pm = true;
    - } else {
    + if (!pci_dev->state_saved)
    + pci_save_state(pci_dev);
    + } else if (!pci_dev->state_saved) {
    pci_save_state(pci_dev);
    if (pci_power_manageable(pci_dev))
    pci_prepare_to_sleep(pci_dev);
    @@ -853,6 +850,22 @@ static int pci_pm_suspend_noirq(struct device *dev)
    dev_dbg(dev, "PCI PM: Suspend power state: %s\n",
    pci_power_name(pci_dev->current_state));

    + if (pci_dev->current_state == PCI_D0) {
    + pci_dev->skip_bus_pm = true;
    + /*
    + * Per PCI PM r1.2, table 6-1, a bridge must be in D0 if any
    + * downstream device is in D0, so avoid changing the power state
    + * of the parent bridge by setting the skip_bus_pm flag for it.
    + */
    + if (pci_dev->bus->self)
    + pci_dev->bus->self->skip_bus_pm = true;
    + }
    +
    + if (pci_dev->skip_bus_pm && !pm_suspend_via_firmware()) {
    + dev_dbg(dev, "PCI PM: Skipped\n");
    + goto Fixup;
    + }
    +
    pci_pm_set_unknown_state(pci_dev);

    /*
    @@ -900,7 +913,16 @@ static int pci_pm_resume_noirq(struct device *dev)
    if (dev_pm_smart_suspend_and_suspended(dev))
    pm_runtime_set_active(dev);

    - pci_pm_default_resume_early(pci_dev);
    + /*
    + * In the suspend-to-idle case, devices left in D0 during suspend will
    + * stay in D0, so it is not necessary to restore or update their
    + * configuration here and attempting to put them into D0 again may
    + * confuse some firmware, so avoid doing that.
    + */
    + if (!pci_dev->skip_bus_pm || pm_suspend_via_firmware())
    + pci_pm_default_resume_early(pci_dev);
    +
    + pci_fixup_device(pci_fixup_resume_early, pci_dev);

    if (pci_has_legacy_pm_support(pci_dev))
    return pci_legacy_resume_early(dev);
    @@ -1201,6 +1223,7 @@ static int pci_pm_restore_noirq(struct device *dev)
    }

    pci_pm_default_resume_early(pci_dev);
    + pci_fixup_device(pci_fixup_resume_early, pci_dev);

    if (pci_has_legacy_pm_support(pci_dev))
    return pci_legacy_resume_early(dev);
    --
    2.20.1


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