Re: [RFC PATCH] PCIe: Add PCIe runtime D3cold support

huang ying
2012-04-20T00:48:23Z

On Thu, Apr 19, 2012 at 8:31 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> 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.

That is better. But as the first step, I prefer the simpler way to
just resume the device. In this way, the synchronization between
remote resume, host resume and system suspend can be easier.

>> 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.

Yes. That is something like power domain, if the power resources are
shared by multiple devices.

Best Regards,
Huang Ying
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