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SubjectRe: Intel GemniLake xHCI connected devices can never wake up the system from suspend
> I've studied the ACPI spec trying to understand better, but I'm
> struggling with the question:
> What is the maximum number (lowest power) permitted device power state
> for a device that is configured as able to wake the system from S3,
> **that does not implement the _S3W method**?

Actually the ACPI spec has an answer for the case when _S3D is present.
The lack of clarity is only over the situation when both _S3D and _S3W
are missing - like on the platforms being worked on here.

The _S3D docs say:
> If the device can wake the system from the S3 system sleeping state (see
> _PRW) then the device must support wake in the D-state returned by this
> object. However, OSPM cannot assume wake from the S3 system sleeping state
> is supported in any deeper D-state unless specified by a corresponding
> _S3W object

Looking at the design of the existing Linux code, it seems like this
"max = min" assignment that is causing us trouble originates directly
from an attempt to implement that logic: if we didn't get a response from
_S3W, then we must clamp ourselves to the data we got from _S3D.

If I modify the Linux code to be a little more specific in that logic
(only applying when we actually got something from _S3D) then the
problematic behaviour is avoided and USB wakeups work.

I feel that this change makes the Linux implementation more directly
mirror the wording in the ACPI spec and it's associated lack of clarity
for when both methods are missing. Thoughts?

drivers/acpi/device_pm.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
index a4c8ad98560d..44f12c5c75ee 100644
--- a/drivers/acpi/device_pm.c
+++ b/drivers/acpi/device_pm.c
@@ -543,6 +543,7 @@ static int acpi_dev_pm_get_state(struct device *dev, struct acpi_device *adev,
unsigned long long ret;
int d_min, d_max;
bool wakeup = false;
+ acpi_status sxd_status;
acpi_status status;

@@ -565,8 +566,8 @@ static int acpi_dev_pm_get_state(struct device *dev, struct acpi_device *adev,
* provided if AE_NOT_FOUND is returned.
ret = d_min;
- status = acpi_evaluate_integer(handle, method, NULL, &ret);
- if ((ACPI_FAILURE(status) && status != AE_NOT_FOUND)
+ sxd_status = acpi_evaluate_integer(handle, method, NULL, &ret);
+ if ((ACPI_FAILURE(sxd_status) && sxd_status != AE_NOT_FOUND)
|| ret > ACPI_STATE_D3_COLD)
return -ENODATA;

@@ -599,7 +600,11 @@ static int acpi_dev_pm_get_state(struct device *dev, struct acpi_device *adev,
method[3] = 'W';
status = acpi_evaluate_integer(handle, method, NULL, &ret);
if (status == AE_NOT_FOUND) {
- if (target_state > ACPI_STATE_S0)
+ /* No _SxW. In this case, the ACPI spec says that we
+ * must not go into any power state deeper than the
+ * value returned from _SxD.
+ */
+ if (sxd_status == AE_OK && target_state > ACPI_STATE_S0)
d_max = d_min;
} else if (ACPI_SUCCESS(status) && ret <= ACPI_STATE_D3_COLD) {
/* Fall back to D3cold if ret is not a valid state. */
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