linux-kernel - Re: [PATCH 1/2] PCI: Avoid runtime resuming devices if system is shutting down

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Message-ID: <d03fd5a4-4f22-45e3-94b1-7ba735ea196f@amd.com>
Date:   Wed, 13 Dec 2023 12:33:08 -0600
From:   Mario Limonciello <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, mpearson-lenovo@...ebb.ca
Subject: Re: [PATCH 1/2] PCI: Avoid runtime resuming devices if system is
 shutting down

On 12/13/2023 12:31, Rafael J. Wysocki wrote:
> On Wed, Dec 13, 2023 at 7:27 PM Mario Limonciello
> <mario.limonciello@....com> wrote:
>>
>> When the system is going to S5 resuming devices is unnecessary at
>> best and may cause problems for power consumption at S5 at worst.
>>
>> Check the target `system_state` in the pci driver shutdown() callback
>> and skip the runtime resume step if the system is being powered off.
>>
>> Cc: mpearson-lenovo@...ebb.ca
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>>   drivers/pci/pci-driver.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>> index 51ec9e7e784f..5a6f7a786952 100644
>> --- a/drivers/pci/pci-driver.c
>> +++ b/drivers/pci/pci-driver.c
>> @@ -507,7 +507,9 @@ static void pci_device_shutdown(struct device *dev)
>>          struct pci_dev *pci_dev = to_pci_dev(dev);
>>          struct pci_driver *drv = pci_dev->driver;
>>
>> -       pm_runtime_resume(dev);
>> +       /* If system will go to S5, don't wake up PCI devices for shutdown */
>> +       if (system_state != SYSTEM_POWER_OFF)
>> +               pm_runtime_resume(dev);
> 
> What's the guarantee that the driver's shutdown callback will not
> access MMIO regions of a runtime-suspended device?

This is something that may need to be audited.

I have an expectation that drivers will runtime resume a device before 
they try to access it.

> 
>>          if (drv && drv->shutdown)
>>                  drv->shutdown(pci_dev);
>> --