Refactored the validation code

- The check is active regardless of the USE_UNCOMMON_MIXER to detect
unsupported/insufficiently supported mixers.
- Custom mixers always pass the check.
- Mixer mode resets to MIXER_CUSTOM if motorCount != 0 but motor array
is NULL.
- Mixer mode resets to MIXER_CUSTOM_AIRPLANE if useServo but servo
count is zero.

src/main/fc/config.c

@@ -546,11 +546,19 @@ void activateConfig(void)
 
 void validateAndFixConfig(void)
 {
-#if !defined(USE_UNCOMMON_MIXERS) && !defined(USE_QUAD_MIXER_ONLY) && !defined(USE_OSD_SLAVE)
+#if !defined(USE_QUAD_MIXER_ONLY) && !defined(USE_OSD_SLAVE)
+    // Reset unsupported mixer mode to default.
+    // This check will be gone when motor/servo mixers are loaded dynamically
+    // by configurator as a part of configuration procedure.
+
     mixerMode_e mixerMode = mixerConfigMutable()->mixerMode;
 
-    if (mixerMode != MIXER_CUSTOM && mixerMode != MIXER_CUSTOM_AIRPLANE && mixerMode != MIXER_CUSTOM_TRI && mixerMode != MIXER_GIMBAL && mixerMode != MIXER_PPM_TO_SERVO && mixers[mixerMode].motor == NULL) {
+    if (!(mixerMode == MIXER_CUSTOM || mixerMode == MIXER_CUSTOM_AIRPLANE || mixerMode == MIXER_CUSTOM_TRI)) {
+        if (mixers[mixerMode].motorCount && mixers[mixerMode].motor == NULL)
             mixerConfigMutable()->mixerMode = MIXER_CUSTOM;
+
+        if (mixers[mixerMode].useServo && servoMixers[mixerMode].servoRuleCount == 0)
+            mixerConfigMutable()->mixerMode = MIXER_CUSTOM_AIRPLANE;
     }
 #endif
 

src/main/flight/servos.c

@@ -148,13 +148,6 @@ static const servoMixer_t servoMixerGimbal[] = {
     { SERVO_GIMBAL_ROLL, INPUT_GIMBAL_ROLL,  125, 0, 0, 100, 0 },
 };
 
-
-// Custom mixer configuration
-typedef struct mixerRules_s {
-    uint8_t servoRuleCount;
-    const servoMixer_t *rule;
-} mixerRules_t;
-
 const mixerRules_t servoMixers[] = {
     { 0, NULL },                // entry 0
     { COUNT_SERVO_RULES(servoMixerTri), servoMixerTri },       // MULTITYPE_TRI

src/main/flight/servos.h

@@ -91,6 +91,14 @@ typedef struct servoMixer_s {
 
 PG_DECLARE_ARRAY(servoMixer_t, MAX_SERVO_RULES, customServoMixers);
 
+// Custom mixer configuration
+typedef struct mixerRules_s {
+    uint8_t servoRuleCount;
+    const servoMixer_t *rule;
+} mixerRules_t;
+
+extern const mixerRules_t servoMixers[];
+
 typedef struct servoParam_s {
     uint32_t reversedSources;               // the direction of servo movement for each input source of the servo mixer, bit set=inverted
     int16_t min;                            // servo min