Re: [PATCH v4] PCI: Call _REG when transitioning D-states

Rafael J. Wysocki
2023-06-21T11:26:16Z

On Tue, Jun 20, 2023 at 4:23 PM Mario Limonciello
<mario.limonciello@amd.com> wrote:
>
> Section 6.5.4 of the ACPI 6.4 spec describes how AML is unable to access
> an OperationRegion unless `_REG` has been called.
>
> "The OS runs _REG control methods to inform AML code of a change in the
> availability of an operation region. When an operation region handler
> is unavailable, AML cannot access data fields in that region.
> (Operation region writes will be ignored and reads will return
> indeterminate data.)"
>
> The PCI core does not call `_REG` at anytime, leading to the undefined
> behavior mentioned in the spec.
>
> The spec explains that _REG should be executed to indicate whether a
> given region can be accessed.
>
> "Once _REG has been executed for a particular operation region, indicating
> that the operation region handler is ready, a control method can
> access fields in the operation region. Conversely, control methods
> must not access fields in operation regions when _REG method execution
> has not indicated that the operation region handler is ready."
>
> An example included in the spec demonstrates calling _REG when devices are
> turned off: "when the host controller or bridge controller is turned off
> or disabled, PCI Config Space Operation Regions for child devices are
> no longer available. As such, ETH0’s _REG method will be run when it
> is turned off and will again be run when PCI1 is turned off.".
>
> It is reported that ASMedia PCIe GPIO controllers fail functional tests
> after the system has returning from suspend (S3 or s2idle). This is
> because the BIOS checks whether the OSPM has called the `_REG` method
> to determine whether it can interact with the OperationRegion assigned
> to the device as part of the other AML called for the device.
>
> To fix this issue, call acpi_evaluate_reg() when devices are
> transitioning to D3cold or D0.
>
> Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/06_Device_Configuration/Device_Configuration.html#reg-region
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> v3->v4:
> * Only enable config space access for D0 state instead of D1/D2 states.
> * Only disallow config space access for D3cold state.

I would ACPI to the patch subject, like "PCI: ACPI: Call ...", but
that can be done when applying the patch, and it is the only comment I
have to this version, so

Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>

> v2->v3:
> * Move call site
> * Rename static function to better describe behavior
> * call _REG with disconnect /before/ going into D3
> * call _REG with connect /after/ going into D0/D1/D2
> * Update commit message
> v1->v2:
> * Handle case of no CONFIG_ACPI
> * Rename function
> * Update commit message
> * Move ACPI calling code into pci-acpi.c instead
> * Cite the ACPI spec
> ---
> drivers/pci/pci-acpi.c | 44 ++++++++++++++++++++++++++++--------------
> 1 file changed, 29 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 052a611081ec..182cac535250 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1043,6 +1043,16 @@ bool acpi_pci_bridge_d3(struct pci_dev *dev)
> return false;
> }
>
> +static void acpi_pci_config_space_access(struct pci_dev *dev, bool enable)
> +{
> + int val = enable ? ACPI_REG_CONNECT : ACPI_REG_DISCONNECT;
> + int ret = acpi_evaluate_reg(ACPI_HANDLE(&dev->dev),
> + ACPI_ADR_SPACE_PCI_CONFIG, val);
> + if (ret)
> + pci_dbg(dev, "ACPI _REG %s evaluation failed (%d)\n",
> + enable ? "connect" : "disconnect", ret);
> +}
> +
> int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)
> {
> struct acpi_device *adev = ACPI_COMPANION(&dev->dev);
> @@ -1053,32 +1063,36 @@ int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)
> [PCI_D3hot] = ACPI_STATE_D3_HOT,
> [PCI_D3cold] = ACPI_STATE_D3_COLD,
> };
> - int error = -EINVAL;
> + int ret;
>
> /* If the ACPI device has _EJ0, ignore the device */
> if (!adev || acpi_has_method(adev->handle, "_EJ0"))
> return -ENODEV;
>
> switch (state) {
> + case PCI_POWER_ERROR:
> + case PCI_UNKNOWN:
> + return -EINVAL;
> case PCI_D3cold:
> if (dev_pm_qos_flags(&dev->dev, PM_QOS_FLAG_NO_POWER_OFF) ==
> - PM_QOS_FLAGS_ALL) {
> - error = -EBUSY;
> - break;
> - }
> - fallthrough;
> - case PCI_D0:
> - case PCI_D1:
> - case PCI_D2:
> - case PCI_D3hot:
> - error = acpi_device_set_power(adev, state_conv[state]);
> + PM_QOS_FLAGS_ALL)
> + return -EBUSY;
> + /* Notify AML lack of PCI config space availability */
> + acpi_pci_config_space_access(dev, false);
> + break;
> }
>
> - if (!error)
> - pci_dbg(dev, "power state changed by ACPI to %s\n",
> - acpi_power_state_string(adev->power.state));
> + ret = acpi_device_set_power(adev, state_conv[state]);
> + if (ret)
> + return ret;
> + pci_dbg(dev, "power state changed by ACPI to %s\n",
> + acpi_power_state_string(adev->power.state));
>
> - return error;
> + /* Notify AML of PCI config space availability */
> + if (state == PCI_D0)
> + acpi_pci_config_space_access(dev, true);
> +
> + return 0;
> }
>
> pci_power_t acpi_pci_get_power_state(struct pci_dev *dev)
> --
> 2.34.1
>