Re: [PATCH v3 1/3] PCI / ACPI: Use cached ACPI device state to get PCI device power state

["Rafael J. Wysocki" <rafael@kernel.org>]

On Tue, Jun 25, 2019 at 12:30 PM Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
>
> The ACPI power state returned by acpi_device_get_power() may depend on
> the configuration of ACPI power resources in the system which may change
> any time after acpi_device_get_power() has returned, unless the
> reference counters of the ACPI power resources in question are set to
> prevent that from happening. Thus it is invalid to use acpi_device_get_power()
> in acpi_pci_get_power_state() the way it is done now and the value of
> the ->power.state field in the corresponding struct acpi_device objects
> (which reflects the ACPI power resources reference counting, among other
> things) should be used instead.
>
> As an example where this becomes an issue is Intel Ice Lake where the
> Thunderbolt controller (NHI), two PCIe root ports (RP0 and RP1) and xHCI
> all share the same power resources. The following picture with power
> resources marked with [] shows the topology:
>
>   Host bridge
>     |
>     +- RP0 ---\
>     +- RP1 ---|--+--> [TBT]
>     +- NHI --/   |
>     |            |
>     |            v
>     +- xHCI --> [D3C]
>
> Here TBT and D3C are the shared ACPI power resources. ACPI _PR3() method
> of the devices in question returns either TBT or D3C or both.
>
> Say we runtime suspend first the root ports RP0 and RP1, then NHI. Now
> since the TBT power resource is still on when the root ports are runtime
> suspended their dev->current_state is set to D3hot. When NHI is runtime
> suspended TBT is finally turned off but state of the root ports remain
> to be D3hot. Now when the xHCI is runtime suspended D3C gets also turned
> off. PCI core thus has power states of these devices cached in their
> dev->current_state as follows:
>
>   RP0 -> D3hot
>   RP1 -> D3hot
>   NHI -> D3cold
>   xHCI -> D3cold
>
> If the user now runs lspci for instance, the result is all 1's like in
> the below output (00:07.0 is the first root port, RP0):
>
> 00:07.0 PCI bridge: Intel Corporation Device 8a1d (rev ff) (prog-if ff)
>     !!! Unknown header type 7f
>     Kernel driver in use: pcieport
>
> In short the hardware state is not in sync with the software state
> anymore. The exact same thing happens with the PME polling thread which
> ends up bringing the root ports back into D0 after they are runtime
> suspended.
>
> For this reason, modify acpi_pci_get_power_state() so that it uses the
> ACPI device power state that was cached by the ACPI core. This makes the
> PCI device power state match the ACPI device power state regardless of
> state of the shared power resources which may still be on at this point.
>
> Link: https://lore.kernel.org/r/20190618161858.77834-2-mika.westerberg@linux.intel.com
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/pci/pci-acpi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 1897847ceb0c..b782acac26c5 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -685,7 +685,8 @@ static pci_power_t acpi_pci_get_power_state(struct pci_dev *dev)
>         if (!adev || !acpi_device_power_manageable(adev))
>                 return PCI_UNKNOWN;
>
> -       if (acpi_device_get_power(adev, &state) || state == ACPI_STATE_UNKNOWN)
> +       state = adev->power.state;
> +       if (state == ACPI_STATE_UNKNOWN)
>                 return PCI_UNKNOWN;
>
>         return state_conv[state];
> --

Not that there are two additional issues related to the one fixed by
this patch that need to be addressed differently.

For details, see

https://patchwork.kernel.org/patch/11015379/
https://patchwork.kernel.org/patch/11015391/