kblight: Fix duty/percentage scaling

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

framework_lib/src/chromium_ec/commands.rs

@@ -246,6 +246,16 @@ impl EcRequest<()> for EcRequestPwmSetFanDutyV1 {
 
 pub const PWM_MAX_DUTY: u16 = 0xFFFF;
 
+pub fn percent_to_duty(percent: u8) -> u16 {
+    let duty = percent as u32 * PWM_MAX_DUTY as u32;
+    (duty / 100) as u16
+}
+
+pub fn duty_to_percent(duty: u16) -> u8 {
+    let percent = duty as u32 * 100;
+    (percent / PWM_MAX_DUTY as u32) as u8
+}
+
 #[repr(C, packed)]
 pub struct EcRequestPwmSetDuty {
     /// Duty cycle, min 0, max 0xFFFF

framework_lib/src/chromium_ec/mod.rs

@@ -770,7 +770,7 @@ impl CrosEc {
     /// * `percent` - An integer from 0 to 100. 0 being off, 100 being full brightness
     pub fn set_keyboard_backlight(&self, percent: u8) {
         debug_assert!(percent <= 100);
-        let duty = percent as u16 * (PWM_MAX_DUTY / 100);
+        let duty = percent_to_duty(percent);
 
         let res = EcRequestPwmSetDuty {
             duty,
@@ -816,7 +816,7 @@ impl CrosEc {
             other => other?,
         };
 
-        Ok((kblight.duty / (PWM_MAX_DUTY / 100)) as u8)
+        Ok(duty_to_percent(kblight.duty))
     }
 
     pub fn ps2_emulation_enable(&self, enable: bool) -> EcResult<()> {