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

Bjorn Helgaas
2023-06-21T22:29:08Z

On Tue, Jun 20, 2023 at 09:04:51AM -0500, Mario Limonciello 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.

I got lost in the maze of users of ACPI_ADR_SPACE_PCI_CONFIG, but is
it really true that we never call _REG for PCI config space at all
today?

If so, I guess AML that uses ACPI_ADR_SPACE_PCI_CONFIG won't work
until after we set the relevant device to D0?

Do we explicitly set devices to D0 during enumeration, e.g., somewhere
in the pci_scan_device() path? If not, should we?

If we don't set things to D0 during enumeration, it seems like this
AML won't work until we suspend and resume the device.

Separately, I propose a minor restructuring to avoid the need for
mentioning PCI_POWER_ERROR and PCI_UNKNOWN. Checking for those means
we need to look at the definitions to be sure we cover all cases, and
it also doesn't solve the problem that a caller can pass undefined
pci_power_t values that would index outside the state_conv[].

Possible rework attached below. I also like the fact that it makes
the _REG patch very simple and specific to _REG.

> 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>

> 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)

commit 79d4fdf58711 ("PCI/PM: Validate acpi_pci_set_power_state() parameter")
Author: Bjorn Helgaas <bhelgaas@google.com>
Date: Wed Jun 21 16:36:12 2023 -0500

PCI/PM: Validate acpi_pci_set_power_state() parameter

Previously acpi_pci_set_power_state() assumed the requested power state was
valid (PCI_D0 ... PCI_D3cold). If a caller supplied something else, we
could index outside the state_conv[] array and pass junk to
acpi_device_set_power().

Validate the pci_power_t parameter and return -EINVAL if it's invalid.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 052a611081ec..bf545f719182 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1053,32 +1053,37 @@ 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 error;

/* If the ACPI device has _EJ0, ignore the device */
if (!adev || acpi_has_method(adev->handle, "_EJ0"))
return -ENODEV;

switch (state) {
- 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]);
+ case PCI_D3cold:
+ break;
+ default:
+ return -EINVAL;
}

- if (!error)
- pci_dbg(dev, "power state changed by ACPI to %s\n",
- acpi_power_state_string(adev->power.state));
+ if (state == PCI_D3cold) {
+ if (dev_pm_qos_flags(&dev->dev, PM_QOS_FLAG_NO_POWER_OFF) ==
+ PM_QOS_FLAGS_ALL)
+ return -EBUSY;
+ }

- return error;
+ error = acpi_device_set_power(adev, state_conv[state]);
+ if (error)
+ return error;
+
+ pci_dbg(dev, "power state changed by ACPI to %s\n",
+ acpi_power_state_string(adev->power.state));
+
+ return 0;
}

pci_power_t acpi_pci_get_power_state(struct pci_dev *dev)
commit 746652bd0376 ("PCI/PM: Call _REG when transitioning D-states")
Author: Mario Limonciello <mario.limonciello@amd.com>
Date: Tue Jun 20 09:04:51 2023 -0500

PCI/PM: Call _REG when transitioning D-states

ACPI r6.5, sec 6.5.4, describes how AML is unable to access an
OperationRegion unless _REG has been called to connect a handler:

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 any time, 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
Link: https://lore.kernel.org/r/20230620140451.21007-1-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index bf545f719182..a05350a4e49c 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);
@@ -1074,6 +1084,9 @@ int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)
if (dev_pm_qos_flags(&dev->dev, PM_QOS_FLAG_NO_POWER_OFF) ==
PM_QOS_FLAGS_ALL)
return -EBUSY;
+
+ /* Notify AML lack of PCI config space availability */
+ acpi_pci_config_space_access(dev, false);
}

error = acpi_device_set_power(adev, state_conv[state]);
@@ -1083,6 +1096,15 @@ int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)
pci_dbg(dev, "power state changed by ACPI to %s\n",
acpi_power_state_string(adev->power.state));

+ /*
+ * Notify AML of PCI config space availability. Config space is
+ * accessible in all states except D3cold; the only transitions
+ * that change availability are transitions to D3cold and from
+ * D3cold to D0.
+ */
+ if (state == PCI_D0)
+ acpi_pci_config_space_access(dev, true);
+
return 0;
}