Add manual and battery-aware automatic display refresh switching

compositor/src/backends/power.rs

@@ -0,0 +1,137 @@
+//! Power state for automatic display refresh rates. Device batteries are excluded.
+use std::path::Path;
+
+pub(super) fn battery_percent() -> Option<u8> {
+    read_battery_percent(Path::new("/sys/class/power_supply"))
+}
+
+fn read_battery_percent(root: &Path) -> Option<u8> {
+    let mut entries = std::fs::read_dir(root)
+        .ok()?
+        .flatten()
+        .map(|entry| entry.path())
+        .collect::<Vec<_>>();
+    entries.sort();
+    let read = |path: &Path, name: &str| {
+        std::fs::read_to_string(path.join(name))
+            .ok()
+            .map(|text| text.trim().to_owned())
+    };
+    if entries
+        .iter()
+        .any(|path| read(path, "online").as_deref() == Some("1") && read(path, "type").as_deref() != Some("Battery"))
+    {
+        return None;
+    }
+    entries.iter().find_map(|path| {
+        if read(path, "type").as_deref() != Some("Battery")
+            || read(path, "scope").as_deref() == Some("Device")
+            || read(path, "status").as_deref() != Some("Discharging")
+        {
+            return None;
+        }
+        read(path, "capacity")?
+            .parse::<u8>()
+            .ok()
+            .filter(|percent| *percent <= 100)
+    })
+}
+
+pub(super) fn low_power(previous: bool, battery: Option<u8>) -> bool {
+    battery.is_some_and(|percent| if previous { percent < 35 } else { percent < 30 })
+}
+
+/// Return a new policy only when an active session needs a mode transition.
+/// Inactive samples leave the applied policy intact until activation.
+pub(super) fn policy_change(active: bool, applied: bool, battery: Option<u8>) -> Option<bool> {
+    if !active {
+        return None;
+    }
+    let next = low_power(applied, battery);
+    (next != applied).then_some(next)
+}
+
+/// Keep resolution unchanged and use a supported mode within 1 Hz of 60 Hz.
+/// Panels without such a mode retain their normal refresh rate.
+pub(super) fn low_refresh_mode(size: (u16, u16), modes: &[(u16, u16, i32)]) -> Option<usize> {
+    modes
+        .iter()
+        .enumerate()
+        .filter(|(_, (width, height, refresh))| (*width, *height) == size && (59_000..=61_000).contains(refresh))
+        .min_by_key(|(_, (_, _, refresh))| refresh.abs_diff(60_000))
+        .map(|(index, _)| index)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn activation_rescans_only_for_a_changed_policy() {
+        assert_eq!(policy_change(true, false, Some(50)), None);
+        assert_eq!(policy_change(true, true, Some(32)), None);
+        assert_eq!(policy_change(true, false, Some(29)), Some(true));
+        assert_eq!(policy_change(true, true, None), Some(false));
+    }
+
+    #[test]
+    fn paused_samples_defer_changes_until_activation() {
+        assert_eq!(policy_change(false, false, Some(20)), None);
+        assert_eq!(policy_change(true, false, Some(20)), Some(true));
+        assert_eq!(policy_change(false, true, None), None);
+        assert_eq!(policy_change(true, true, None), Some(false));
+        // A round trip across the threshold while paused needs no rescan.
+        assert_eq!(policy_change(false, false, Some(20)), None);
+        assert_eq!(policy_change(true, false, Some(50)), None);
+    }
+
+    #[test]
+    fn low_refresh_selection_rejects_unsupported_rates_and_preserves_resolution() {
+        let modes = [
+            (2880, 1800, 120_000),
+            (1920, 1080, 60_000),
+            (2880, 1800, 59_940),
+            (2880, 1800, 60_000),
+        ];
+        assert_eq!(low_refresh_mode((2880, 1800), &modes), Some(3));
+        assert_eq!(low_refresh_mode((2880, 1800), &modes[..3]), Some(2));
+        assert_eq!(low_refresh_mode((2880, 1800), &modes[..2]), None);
+        assert_eq!(low_refresh_mode((2880, 1800), &[(2880, 1800, -60_000)]), None);
+    }
+
+    #[test]
+    fn thresholds_have_hysteresis_and_ac_or_unknown_restore_normal() {
+        assert!(low_power(false, Some(29)));
+        assert!(!low_power(false, Some(30)));
+        assert!(low_power(true, Some(34)));
+        assert!(!low_power(true, Some(35)));
+        assert!(!low_power(true, None));
+    }
+
+    #[test]
+    fn only_discharging_system_batteries_count_and_ac_has_priority() {
+        let root = tempfile::tempdir().unwrap();
+        let battery = root.path().join("BAT0");
+        std::fs::create_dir(&battery).unwrap();
+        for (name, value) in [
+            ("type", "Battery"),
+            ("scope", "System"),
+            ("status", "Discharging"),
+            ("capacity", "20"),
+        ] {
+            std::fs::write(battery.join(name), value).unwrap();
+        }
+        assert_eq!(read_battery_percent(root.path()), Some(20));
+        std::fs::write(battery.join("scope"), "Device").unwrap();
+        assert_eq!(read_battery_percent(root.path()), None);
+        std::fs::write(battery.join("scope"), "System").unwrap();
+        std::fs::write(battery.join("capacity"), "bad").unwrap();
+        assert_eq!(read_battery_percent(root.path()), None);
+        std::fs::write(battery.join("capacity"), "20").unwrap();
+        let ac = root.path().join("AC");
+        std::fs::create_dir(&ac).unwrap();
+        std::fs::write(ac.join("type"), "Mains").unwrap();
+        std::fs::write(ac.join("online"), "1").unwrap();
+        assert_eq!(read_battery_percent(root.path()), None);
+    }
+}