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    SubjectRe: [RFC PATCH] PCIe: Add PCIe runtime D3cold support
    Date
    On Thursday, April 19, 2012, huang ying wrote:
    > On Thu, Apr 19, 2012 at 5:00 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
    > > On Wednesday, April 18, 2012, huang ying wrote:
    > >> On Wed, Apr 18, 2012 at 5:03 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
    > >> > On Tuesday, April 17, 2012, huang ying wrote:
    > >> >> On Tue, Apr 17, 2012 at 5:30 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
    > >> >> > On Monday, April 16, 2012, huang ying wrote:
    > >> >> >> Hi,
    > >> >> >>
    > >> >> >> On Sat, Apr 14, 2012 at 3:41 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
    > >> >> >> > Hi,
    > >> >> >> >
    > >> >> >> > On Friday, April 13, 2012, Yan, Zheng wrote:
    > >> >> >> >> Hi all,
    > >> >> >> >>
    > >> >> >> >> This patch adds PCIe runtime D3cold support, namely cut power supply for functions
    > >> >> >> >> beneath a PCIe port when they all have entered D3. A device in D3cold can only
    > >> >> >> >> generate wake event through the WAKE# pin. Because we can not access to a device's
    > >> >> >> >> configure space while it's in D3cold, pme_poll is disabled for devices in D3cold.
    > >> >> >> >>
    > >> >> >> >> Any comment will be appreciated.
    > >> >> >> >>
    > >> >> >> >> Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
    > >> >> >> >> ---
    > >> >> >> >> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
    > >> >> >> >> index 0f150f2..e210e8cb 100644
    > >> >> >> >> --- a/drivers/pci/pci-acpi.c
    > >> >> >> >> +++ b/drivers/pci/pci-acpi.c
    > >> >> >> >> @@ -224,7 +224,7 @@ static int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)
    > >> >> >> >> [PCI_D1] = ACPI_STATE_D1,
    > >> >> >> >> [PCI_D2] = ACPI_STATE_D2,
    > >> >> >> >> [PCI_D3hot] = ACPI_STATE_D3,
    > >> >> >> >> - [PCI_D3cold] = ACPI_STATE_D3
    > >> >> >> >> + [PCI_D3cold] = ACPI_STATE_D3_COLD
    > >> >> >> >> };
    > >> >> >> >> int error = -EINVAL;
    > >> >> >> >>
    > >> >> >> >
    > >> >> >> > Please don't use that ACPI_STATE_D3_COLD thing, it's not defined correctly.
    > >> >> >> >
    > >> >> >> > We should define ACPI_STATE_D3_COLD == ACPI_STATE_D3 and add ACPI_STATE_D3_HOT
    > >> >> >> > instead. I'll prepare a patch for that over the weekend if no one has done
    > >> >> >> > that already.
    > >> >> >> >
    > >> >> >> >> @@ -296,7 +296,8 @@ static void acpi_pci_propagate_run_wake(struct pci_bus *bus, bool enable)
    > >> >> >> >>
    > >> >> >> >> static int acpi_pci_run_wake(struct pci_dev *dev, bool enable)
    > >> >> >> >> {
    > >> >> >> >> - if (dev->pme_interrupt)
    > >> >> >> >> + /* PME interrupt isn't available in the D3cold case */
    > >> >> >> >> + if (dev->pme_interrupt && !dev->runtime_d3cold)
    > >> >> >> >
    > >> >> >> > This whole thing is wrong. First off, I don't think that the runtime_d3cold
    > >> >> >> > flag makes any sense. We already cover that in dev->pme_support.
    > >> >> >>
    > >> >> >> PCIe devices and PCIe root port may have proper PME interrupt support
    > >> >> >> (that is, dev->pme_interrupt = true), but the process of remote wakeup
    > >> >> >> from D3cold is as follow:
    > >> >> >>
    > >> >> >> 1) In D3cold, the power of the main link is turned off, aux power is
    > >> >> >> provided (PCIe L2 link state)
    > >> >> >> 2) Device detect condition to resume, then assert #WAKE pin
    > >> >> >> 2) ACPI circuit linked with #WAKE pin, and will generate a GPE for that
    > >> >> >> 3) GPE handler will resume device with ACPI (via _PS3 and _PR0), the
    > >> >> >> power of the main link is turned on, after a while, link goes into L0
    > >> >> >> state
    > >> >> >> 4) The PME message is sent to root port, pme interrupt generated
    > >> >> >
    > >> >> > This isn't how it's supposed to work in theory. If the device can signal PME
    > >> >> > from D3cold, it should be able to reestablish the link and send a PME
    > >> >> > message from there. dev->pme_interrupt set means exactly that.
    > >> >> >
    > >> >> > ACPI is only supposed to be needed for things that don't send PME
    > >> >> > messages (in your case the PME interrupt generated by the port is essentially
    > >> >> > useless, because the wakeup event has already been signaled through ACPI).
    > >> >> >
    > >> >> >> So, for deivce, dev->pme_interrupt = true and dev->pme_support
    > >> >> >> advocate it support PME in D3cold. But we still need ACPI to setup
    > >> >> >> run wake for the device.
    > >> >> >
    > >> >> > OK, so this is nonstandard.
    > >> >>
    > >> >> This is the standard behavior. Please refer to PCI Express Base
    > >> >> Sepcification Revision 2.0, section 5.3.3.2 Link Wakeup. In D1, D2
    > >> >> and D3hot state, PCIe device can transit the link from L1 to L0 state,
    > >> >> and send the PME message. In D3cold, the main link is powered off,
    > >> >> PCIe device will use a STANDARD sideband signal WAKE# to signal wakeup
    > >> >> firstly, then platform (power controller in spec) will power on the
    > >> >> main link for the device, after main link is back to L0, the PME
    > >> >> message is send to root port, pme interrupt is generated. So in
    > >> >> theory, the wake up process can be divided into platform part (which
    > >> >> power on the main link) and PCIe part (which send PME).
    > >> >
    > >> > That's fine. However, the platform part should be completely transparent
    > >> > to the PCI bus type, then. It just should power up the link to allow a
    > >> > PME message to be transmitted through it.
    > >>
    > >> Yes.
    > >>
    > >> >[...]
    > >> >
    > >> >> > So don't use pci_set_power_state() for that, because it's essentially
    > >> >> > a different operation. You need a pci_platform_remove_power() helper or
    > >> >> > similar for that.
    > >> >> >
    > >> >> > What ACPI method exactly is used to remove power from the device?
    > >> >>
    > >> >> The ACPI method executed is as follow:
    > >> >>
    > >> >> - _PS3 (if exist)
    > >> >> - Power resources in _PR3 is turned on
    > >> >> - Power resources in _PR0 is turned off
    > >> >> - Power resources in _PR3 is turned off
    > >> >
    > >> > I'd rather think
    > >> >
    > >> > - make sure that _PR3 resources are referenced
    > >> > - drop references (from this device) for all other power resources
    > >> > - execute _PS3 (if any)
    > >> > - drop references for _PR3 resources
    > >> >
    > >> > if Section 7.2.11 of ACPI 5.0 is to be followed.
    > >>
    > >> Yes. You are right.
    > >>
    > >> >> I think the process can fit pci_set_power_state() quite well, so why
    > >> >> invent another helper for that?
    > >> >
    > >> > OK, we can special case it, perhaps.
    > >> >
    > >> > Suppose we have a "this device may be put into D3_cold" flag.
    > >> >
    > >> > Who's going to decide whether to put it into D3_hot or D3_cold?
    > >>
    > >> In most cases, I think it is OK to put device into D3_cold if that is
    > >> supported.
    > >
    > > Well, there may be PM QoS latency requirements preventing us from doing so.
    >
    > Yes.
    >
    > >> But there should be some special case where D3_cold is not
    > >> desirable, for example, we can put SSD into D3_cold safely, but it is
    > >> not quite safe to put HDD into D3_cold. So we want to introduce a
    > >> flag: "may_power_off" like in the following patch
    > >>
    > >> https://lkml.org/lkml/2012/3/29/41
    > >>
    > >> It gives device driver a chance to prevent the device to be put into D3_cold.
    > >
    > > I see. So your proposal is that the flag might be used to indicate to
    > > whoever carries out power transitions of devices that power must not be
    > > removed from this particular device, right?
    >
    > Yes.
    >
    > > In that case we can put that flag into struct dev_pm_info after all, but
    > > perhaps the name should indicate more precisely what it is about. Something
    > > like "power_must_be_on" maybe?
    >
    > I am not good at naming in English :)
    > I will accept your proposal.
    >
    > >> > [...]
    > >> >
    > >> >> >> > So now please tell me what exactly you want to achieve and why you want to do
    > >> >> >> > that in the first place.
    > >> >> >
    > >> >> > Well, is there any chance to get that information?
    > >> >>
    > >> >> You mean the runtime_d3cold flag? That flag is used to tell
    > >> >> acpi_pci_run_wake() that we need ACPI wakeup setup for the device
    > >> >> because that is needed by D3cold. The ACPI wakeup setup here means
    > >> >> turn on power resources needed by wake up (_PRW) and execute _DSW.
    > >> >>
    > >> >> If you mean the whole patch, we want to implement runtime D3cold
    > >> >> support, which can save more power than D3hot.
    > >> >
    > >> > So, do I think correctly that you'd like to put devices into D3_cold
    > >> > if that's possible via ACPI and to be able to wake it up from that state
    > >> > using remote wakeup?
    > >>
    > >> Yes. Support both remote wakeup and host wakeup.
    > >
    > > OK, so we need to clean up the ACPI D3_HOT/D3_COLD mess first. Then, we need
    > > to change PCI so that devices are not put into D3cold (by ACPI) if only D3hot
    > > is requested by the caller of pci_set_power_state().
    > >
    > > Having done that, we can modify pci_set_power_state() to handle D3cold as
    > > a special case (essentially, it should check that case before doing anything
    > > else). Finally, we need to teach the ACPI notify handler about the WAKE#
    > > event and we need to add the 100 ms wait to the device resume code path
    > > somewhere (I guess in pci_set_power_state() for the D3cold->D0 transition).
    >
    > Yes. Sound good to me.
    >
    > > Now, there's one more thing to consider. Namely, if a PCIe endpoint is put
    > > into D3hot (via native PM) and then the port it is connected to is put into
    > > D3_hot (via native PM), does that transfer the endpoint into D3cold?
    >
    > No.
    >
    > But if a PCIe endpoint is put into D3hot and then the port it is
    > connected is put into D3_cold (via ACPI), this will transfer the
    > endpoint into D3_cold, and if the port is put into D0 afterwards, all
    > subordinate endpoint devices will be put into D0 (because of power on
    > reset). I think what we need to do here is:
    >
    > - when choose power state, if any subordinate device has
    > power_must_be_on set, will not choose D3_cold

    Well, that's quite obvious. :-)

    > - when put PCIe port from D3_cold to D0, resume all subordinate
    > devices too.

    Alternatively, we can just call pci_restore_state() on them and put
    them into PCI_D3hot again without actually resuming.

    > We design a method to do that in following patch:
    >
    > https://lkml.org/lkml/2012/3/29/38
    >
    > Where we will register all subordinate devices via
    > acpi_power_resource_register_device(endpoint_device,
    > bridget_acpi_handle).

    I think that's overkill in the case of PCI devices under a PCIe port.
    We only need to walk the bus below the port and do something for each device
    in there then.

    Thanks,
    Rafael


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