Messages in this thread | | | Date | Tue, 18 Oct 2011 19:22:21 +0530 | From | Ajaykumar Hotchandani <> | Subject | Re: [PATCH] PCI: Set device power state to PCI_D0 for device without native PM support |
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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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