power_manager/docs/machine_quirks.md

# Power Manager Machine Quirks

## Introduction

The role of Machine Quirks is to read DMI info from the kernel at runtime, and then activate the relevant prefs to that machine. This is necessary for the use case of the reven board, that supports a wide range of devices from different manufacturers. Further background can be found at [go/machine-quirks-design](go/machine-quirks-design).

## Design & Implementation Details

On the machine, when powerd initializes, first it checks if the `kHasMachineQuirksPref` is activated by the board to see if it should move on.

Next, the [MachineQuirks class](https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/power_manager/powerd/system/machine_quirks.cc) collects DMI info from the following location:
```
/sys/class/dmi/id/product_name
```

It compares the value of `product_name` with the `kSuspendToIdleListPref` and the `kSuspendPreventionListPref`. If a match is found, then either `kSuspendToIdlePref` or `kDisableIdleSuspendPref` is set to true via the Prefs class.

### Code:
[machine_quirks.h](https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/power_manager/powerd/system/machine_quirks.h)\
[machine_quirks.cc](https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/power_manager/powerd/system/machine_quirks.cc)\
[machine_quirks_stub.cc](https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/power_manager/powerd/system/machine_quirks_stub.cc)\
[machine_quirks_stub.h](https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/power_manager/powerd/system/machine_quirks_stub.h)\
[machine_quirks_test.cc](https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/power_manager/powerd/system/machine_quirks_test.cc)

### Activation in Overlay

The MachineQuirks feature is currently activated via `chromeos-config` in the overlay, using `model.yaml` in `chromeos-config-bsp`.
In the future, activation may be moved to boxster.

## Testing

The machine quirk lists can be modified by creating files in `/var/lib/power_manager` to test out device fixes\*.

### Test suspend_to_idle_models
```
cat /sys/class/dmi/id/product_name > /var/lib/power_manager/suspend_to_idle_models
restart powerd
```
Refer to logs in `/var/log/power_manager/powerd.LATEST` and look at arguments passed into `powerd_setuid_helper` to confirm if the `--suspend-to-idle` flag was passed.

```
# after test, clear settings again
rm /var/lib/power_manager/suspend_to_idle_models
restart powerd
```
### Test suspend_prevention_models
```
cat /sys/class/dmi/id/product_name > /var/lib/power_manager/suspend_prevention_models
restart powerd
```
When suspend prevention is enabled, after suspend the power button remains on, and the screen immediately turns on upon user interaction on the keyboard.
```
# after test, clear settings again
rm /var/lib/power_manager/suspend_prevention_models
restart powerd
```

\*`has_machine_quirks` should be set to 1 for the above to work.