Re: [PATCH] PCI: Fix the ACPI power state during runtime resume

Bjorn Helgaas
2022-02-04T23:32:25Z

[+cc Rafael, hoping for your review :)

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_]*\(

DYNAMIC THERMAL POWER MANAGEMENT (DTPM)
M: Daniel Lezcano <daniel.lezcano@kernel.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.
>
> 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. 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@nvidia.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.
> + */
> + error = pci_power_up(pci_dev);
> }
>
> + if (error)
> + return error;
> +
> pci_restore_state(pci_dev);
> pci_pme_restore(pci_dev);
> return 0;
> --
> 2.17.1
>