Date:   Tue, 5 Apr 2022 22:06:34 +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 4:00 PM, Abhishek Sahu wrote:
> 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
> 

 Hi Rafael/Mika,

 Could you please help regarding the correct way to fix this issue.
 I can update the patch accordingly.
 
 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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