Date:   Tue, 8 Feb 2022 16:00:35 +0530
From:   Abhishek Sahu <abhsahu@...dia.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Linux PM <linux-pm@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH] PCI: Fix the ACPI power state during runtime resume

On 2/8/2022 12:28 AM, Rafael J. Wysocki wrote:
> On Saturday, February 5, 2022 12:32:19 AM CET Bjorn Helgaas wrote:
>> [+cc Rafael, hoping for your review :)
> 
> +Mika
> 
>> Wonder if we should add something like this to MAINTAINERS so you get
>> cc'd on power-related things:
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index ea3e6c914384..3d9a211cad5d 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -15422,6 +15422,7 @@ F:    include/linux/pm.h
>>  F:   include/linux/pm_*
>>  F:   include/linux/powercap.h
>>  F:   kernel/configs/nopm.config
>> +K:   pci_[a-z_]*power[a-z_]*\(
> 
> It seems so, but generally PM patches should be CCed to linux-pm anyway.
> 
>>
>>  DYNAMIC THERMAL POWER MANAGEMENT (DTPM)
>>  M:   Daniel Lezcano <daniel.lezcano@...nel.org>
>> ]
>>
>> On Mon, Jan 24, 2022 at 05:51:07PM +0530, Abhishek Sahu wrote:
>>> Consider the following sequence during PCI device runtime
>>> suspend/resume:
>>>
>>> 1. PCI device goes into runtime suspended state. The PCI state
>>>    will be changed to PCI_D0 and then pci_platform_power_transition()
>>>    will be called which changes the ACPI state to ACPI_STATE_D3_HOT.
> 
> You mean PCI_D3hot I suppose?
>

 Yes. It should be PCI_D3hot here. 

>>> 2. Parent bridge goes into runtime suspended state. If parent
>>>    bridge supports D3cold, then it will change the power state of all its
>>>    children to D3cold state and the power will be removed.
>>>
>>> 3. During wake-up time, the bridge will be runtime resumed first
>>>    and pci_power_up() will be called for the bridge. Now, the power
>>>    supply will be resumed.
>>>
>>> 4. pci_resume_bus() will be called which will internally invoke
>>>    pci_restore_standard_config(). pci_update_current_state()
>>>    will read PCI_PM_CTRL register and the current_state will be
>>>    updated to D0.
>>>
>>> In the above process, at step 4, the ACPI device state will still be
>>> ACPI_STATE_D3_HOT since pci_platform_power_transition() is not being
>>> invoked.
> 
> I'm not quite following.
> 
> I'm assuming that this description applies to the endpoint device that was
> previously put into D3_hot.
> 

 Yes. This is applicable for endpoint devices which was previously put
 into D3hot.

> Since its current state is D3_hot, it is not D0 (in particular) and the
> pci_set_power_state() in pci_restore_standard_config() should put int into
> D0 proper, including the platform firmware part.
> 

 The pci_restore_standard_config() for endpoint devices are being called
 internally during wake-up of upstream bridge. 

 pci_power_up(struct pci_dev *dev)
 {
      ...
      if (dev->runtime_d3cold) {
        /*
         * When powering on a bridge from D3cold, the whole hierarchy
         * may be powered on into D0uninitialized state, resume them to
         * give them a chance to suspend again
         */
        pci_resume_bus(dev->subordinate);
    }
    ...
 }

 For the upstream bridge, the above code will trigger the wake-up of
 endpoint devices and then following code will be executed for the
 endpoint devices:

 pci_update_current_state(struct pci_dev *dev, pci_power_t state)
 {
    if (platform_pci_get_power_state(dev) == PCI_D3cold ||
        !pci_device_is_present(dev)) {
        dev->current_state = PCI_D3cold;
    } else if (dev->pm_cap) {
        u16 pmcsr;

        pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
        dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK);
    } else {
        dev->current_state = state;
    }
 }

 In the above code, the current_state will be set to D0 for the
 endpoint devices since it will go into second block where
 it will read the PM_CTRL register.
 
>>> We need call the pci_platform_power_transition() with state
>>> D0 to change the ACPI state to ACPI_STATE_D0.
>>>
>>> This patch calls pci_power_up() if current power state is D0 inside
>>> pci_restore_standard_config(). This pci_power_up() will change the
>>> ACPI state to ACPI_STATE_D0.
>>>
>>> Following are the steps to confirm:
>>>
>>> Enable the debug prints in acpi_pci_set_power_state()
>>>
>>> 0000:01:00.0 is PCI device and 0000:00:01.0 is parent bridge device
>>>
>>> Before:
>>>
>>> 0000:01:00.0: power state changed by ACPI to D3hot
>>> 0000:00:01.0: power state changed by ACPI to D3cold
>>> 0000:00:01.0: power state changed by ACPI to D0
>>>
>>> After:
>>>
>>> 0000:01:00.0: power state changed by ACPI to D3hot
>>> 0000:00:01.0: power state changed by ACPI to D3cold
>>> 0000:00:01.0: power state changed by ACPI to D0
>>> 0000:01:00.0: power state changed by ACPI to D0
>>>
>>> So with this patch, the PCI device ACPI state is also being
>>> changed to D0.
>>>
>>> Signed-off-by: Abhishek Sahu <abhsahu@...dia.com>
>>> ---
>>>  drivers/pci/pci-driver.c | 14 +++++++++++---
>>>  1 file changed, 11 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>>> index 588588cfda48..64e0cca12f16 100644
>>> --- a/drivers/pci/pci-driver.c
>>> +++ b/drivers/pci/pci-driver.c
>>> @@ -521,14 +521,22 @@ static void pci_device_shutdown(struct device *dev)
>>>   */
>>>  static int pci_restore_standard_config(struct pci_dev *pci_dev)
>>>  {
>>> +   int error = 0;
>>>     pci_update_current_state(pci_dev, PCI_UNKNOWN);
>>>
>>>     if (pci_dev->current_state != PCI_D0) {
>>> -           int error = pci_set_power_state(pci_dev, PCI_D0);
>>> -           if (error)
>>> -                   return error;
>>> +           error = pci_set_power_state(pci_dev, PCI_D0);
>>> +   } else {
>>> +           /*
>>> +            * The platform power state can still be non-D0, so this is
>>> +            * required to change the platform power state to D0.
>>> +            */
> 
> This really isn't expected to happen.
> 
> If the device's power state has been changed to D3hot by ACPI, it is not in D0.
> 
> It looks like the state tracking is not working here.
> 

 The state setting to D0 is happening due to the current logic present in
 pci_update_current_state(). If we can fix the logic in
 pci_update_current_state() to detect this condition and return state D3hot,
 then it should also fix the issue. 

 Thanks,
 Abhishek

>>> +           error = pci_power_up(pci_dev);
>>>     }
>>>
>>> +   if (error)
>>> +           return error;
>>> +
>>>     pci_restore_state(pci_dev);
>>>     pci_pme_restore(pci_dev);
>>>     return 0;
>>
> 
> 
> 
> 

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