acpi: Report RPM values instead of raw tachometer values

Ref: IT5570E V0.3.2 datasheet; 7.12.3.2 Manual Fan Control Mode
Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/acpi.c

@@ -7,9 +7,9 @@
 #include <board/kbled.h>
 #include <board/lid.h>
 #include <board/peci.h>
-#include <common/macro.h>
+#include <board/pwm.h>
 #include <common/debug.h>
-#include <ec/pwm.h>
+#include <common/macro.h>
 
 #ifndef HAVE_LED_AIRPLANE_N
 #define HAVE_LED_AIRPLANE_N 1
@@ -162,13 +162,11 @@ uint8_t acpi_read(uint8_t addr) {
         ACPI_8(0xCC, sci_extra);
 
         ACPI_8(0xCE, DCR2);
-        ACPI_8(0xD0, F1TLRR);
-        ACPI_8(0xD1, F1TMRR);
+        ACPI_16(0xD0, pwm_tach0_rpm);
 #if CONFIG_HAVE_DGPU
         ACPI_8(0xCD, dgpu_temp);
         ACPI_8(0xCF, DCR4);
-        ACPI_8(0xD2, F2TLRR);
-        ACPI_8(0xD3, F2TMRR);
+        ACPI_16(0xD2, pwm_tach1_rpm);
 #endif // CONFIG_HAVE_DGPU
 
 #if HAVE_LED_AIRPLANE_N

src/board/system76/common/include/board/pwm.h

@@ -5,6 +5,13 @@
 
 #include <ec/pwm.h>
 
+// NOTE: These are used instead of the functions directly for ACPI to prevent
+// double reads of the tachometer values.
+extern int16_t pwm_tach0_rpm;
+extern int16_t pwm_tach1_rpm;
+
 void pwm_init(void);
+int16_t pwm_get_tach0_rpm(void);
+int16_t pwm_get_tach1_rpm(void);
 
 #endif // _BOARD_PWM_H

src/board/system76/common/main.c

@@ -135,6 +135,11 @@ void main(void) {
 
                 // Update fan speeds
                 fan_duty_set(peci_get_fan_duty(), dgpu_get_fan_duty());
+
+                // NOTE: These values are reported to ACPI. Update them at the
+                // same interval as the fan duties.
+                pwm_tach0_rpm = pwm_get_tach0_rpm();
+                pwm_tach1_rpm = pwm_get_tach1_rpm();
             }
 
             // Only run the following once per interval

src/board/system76/common/pwm.c

@@ -3,6 +3,18 @@
 #include <board/pwm.h>
 #include <common/macro.h>
 
+#define TACH_FREQ (CONFIG_CLOCK_FREQ_KHZ * 1000UL)
+
+// Fan Speed (RPM) = 60 / (1/fs sec * {FnTMRR, FnRLRR} * P)
+// - n: 1 or 2
+// - P: the numbers of square pulses per revolution
+// - fs: sample rate (FreqEC / 128)
+// - {FnTMRR, FnTLRR} = 0000h: Fan Speed is zero
+#define TACH_TO_RPM(x) (60UL * TACH_FREQ / 128UL / 2UL / (x))
+
+int16_t pwm_tach0_rpm = -1;
+int16_t pwm_tach1_rpm = -1;
+
 void pwm_init(void) {
     // Set T0CHSEL to TACH0A and T1CHSEL to TACH1A
     TSWCTLR = 0;
@@ -37,3 +49,21 @@ void pwm_init(void) {
     // Enable PWM
     ZTIER = BIT(1);
 }
+
+int16_t pwm_get_tach0_rpm(void) {
+    uint16_t rpm = (F1TMRR << 8) | F1TLRR;
+
+    if (rpm)
+        rpm = TACH_TO_RPM(rpm);
+
+    return rpm;
+}
+
+int16_t pwm_get_tach1_rpm(void) {
+    uint16_t rpm = (F2TMRR << 8) | F2TLRR;
+
+    if (rpm)
+        rpm = TACH_TO_RPM(rpm);
+
+    return rpm;
+}