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    SubjectRe: [PATCH] PCI: Set device power state to PCI_D0 for device without native PM support


    On 10/13/2011 08:00 PM, Stefano Stabellini wrote:
    > On Mon, 10 Oct 2011, Ajaykumar Hotchandani wrote:
    >> On 10/06/2011 09:47 PM, Stefano Stabellini wrote:
    >>> On Thu, 6 Oct 2011, Yinghai Lu wrote:
    >>>> On Thu, Oct 6, 2011 at 3:39 AM, Stefano Stabellini
    >>>> <stefano.stabellini@eu.citrix.com> wrote:
    >>>>> I had the same issue and sent a patch a while ago to fix it, adding
    >>>>>
    >>>>> current_state = PCI_D0 in acpiphp_glue.c:register_slot
    >>>>>
    >>>>> it is strange that this does not work for you:
    >>>>>
    >>>>> http://marc.info/?l=linux-kernel&m=129891002722845&w=2
    >>>> So guest os has to load acpiphp instead of pciehp?
    >>> maybe pciehp needs to make sure that current_state = D0 in
    >>> pciehp_enable_slot, like acpiphp does
    >> Here, acpi hotplugging is involved.
    >> With your change in register_slot(), device will have proper power state when module is being loaded for the first time after booting.
    >> However, while unload of pci module; following is in pci_device_remove():
    >> if (pci_dev->current_state == PCI_D0)
    >> pci_dev->current_state = PCI_UNKNOWN;
    >>
    >> So, device power state state will remain PCI_UNKNOWN while module is loaded again. Subsequently, MSI write will do nothing.
    > Does this mean that this bug would actually trigger even with devices that
    > do support _EJ0 and power management?
    Nope. I don't have system to verify. But, for the scenario you mentioned
    (device is hot pluggable, acpi bus power manageable and device with
    pm_cap supported; if I understand it correctly), following is what I
    think should happen:
    - Inside pci_platform_power_transition(),
    platform_pci_power_manageable() will be successful. However,
    platform_pci_set_power_state() will fail (as device supports EJ0) and
    subsequently pci_update_current_state() will not get called.
    - So, current power state of device will not be read and power state of
    device will remain PCI_UNKNOWN.
    - Now, pci_raw_set_power_state() will get called. Here, as current power
    state is PCI_UNKNOWN, pci_write_config_word() will be called with pmcsr
    value as 0. As, last two bits of pmcsr is 0, written power state of
    device will be PCI_D0 now. And subsequently, dev->current_state will be
    assigned as PCI_D0 (by using pci_read_config_word() ).
    > Because acpi_pci_set_power_state won't set current_state to PCI_D0
    > because the "hotplug driver will take care of _PSx" (see
    > 10b3dcae0f275e2546e55303d64ddbb58cec7599) but the hotplug driver is not
    > actually invoked when loading again a driver module of an existing pci
    > device (the example you mention above)?
    Can you please elaborate more on this?
    acpi_bus_set_power() will update state of acpi_dev (ACPI_STATE_XX) and
    not pci_dev (PCI_XX).
    And here, issue lies with current_state of pci_dev.

    Thanks,
    Ajay



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