pwm: Reload counters when they reach 0

Add IT5570E register that controls when DCRi is updated. Set it to
update when the counter reaches 0, instead of immediately when the
register is written.

Fixes keyboard color when changing brightness levels if not using 0xFF
for an RGB value.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/pwm.c

@@ -26,6 +26,11 @@ void pwm_init(void) {
     // Turn off CPU fan (temperature control in peci_get_fan_duty)
     DCR2 = 0;
 
+#ifdef it5570e
+    // Reload counters when they reach 0 instead of immediately
+    PWMLCCR = 0xFF;
+#endif
+
     // Enable PWM
     ZTIER = BIT(1);
 }

src/ec/ite/include/ec/pwm.h

@@ -62,4 +62,9 @@ volatile uint8_t __xdata __at(0x1823) ZTIER;
 // Tachometer switch control register
 volatile uint8_t __xdata __at(0x1848) TSWCTLR;
 
+#ifdef it5570e
+// PWM Load Counter Control Register
+volatile uint8_t __xdata __at(0x185A) PWMLCCR;
+#endif
+
 #endif // _EC_PWM_H