Improve E_AXIS_N macro

Marlin/src/gcode/feature/trinamic/M911-M915.cpp

   void GcodeSuite::M913() {
     #define TMC_SAY_PWMTHRS(A,Q) tmc_get_pwmthrs(stepper##Q, planner.axis_steps_per_mm[_AXIS(A)])
     #define TMC_SET_PWMTHRS(A,Q) tmc_set_pwmthrs(stepper##Q, value, planner.axis_steps_per_mm[_AXIS(A)])
-    #define TMC_SAY_PWMTHRS_E(E) do{ constexpr uint8_t extruder = E; tmc_get_pwmthrs(stepperE##E, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }while(0)
-    #define TMC_SET_PWMTHRS_E(E) do{ constexpr uint8_t extruder = E; tmc_set_pwmthrs(stepperE##E, value, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }while(0)
+    #define TMC_SAY_PWMTHRS_E(E) tmc_get_pwmthrs(stepperE##E, planner.axis_steps_per_mm[E_AXIS_N(E)])
+    #define TMC_SET_PWMTHRS_E(E) tmc_set_pwmthrs(stepperE##E, value, planner.axis_steps_per_mm[E_AXIS_N(E)])
 
     bool report = true;
     const uint8_t index = parser.byteval('I');

Marlin/src/inc/Conditionals_LCD.h

  */
 #if ENABLED(DISTINCT_E_FACTORS) && E_STEPPERS > 1
   #define XYZE_N (XYZ + E_STEPPERS)
-  #define E_AXIS_N (E_AXIS + extruder)
+  #define E_AXIS_N(E) (E_AXIS + E)
 #else
   #undef DISTINCT_E_FACTORS
   #define XYZE_N XYZE
-  #define E_AXIS_N E_AXIS
+  #define E_AXIS_N(E) E_AXIS
 #endif
 
 /**

Marlin/src/module/planner.cpp

         }
       #endif // PREVENT_COLD_EXTRUSION
       #if ENABLED(PREVENT_LENGTHY_EXTRUDE)
-        if (ABS(de * e_factor[extruder]) > (int32_t)axis_steps_per_mm[E_AXIS_N] * (EXTRUDE_MAXLENGTH)) { // It's not important to get max. extrusion length in a precision < 1mm, so save some cycles and cast to int
+        if (ABS(de * e_factor[extruder]) > (int32_t)axis_steps_per_mm[E_AXIS_N(extruder)] * (EXTRUDE_MAXLENGTH)) { // It's not important to get max. extrusion length in a precision < 1mm, so save some cycles and cast to int
           position[E_AXIS] = target[E_AXIS]; // Behave as if the move really took place, but ignore E part
           #if HAS_POSITION_FLOAT
             position_float[E_AXIS] = target_float[E_AXIS];
     delta_mm[B_AXIS] = db * steps_to_mm[B_AXIS];
     delta_mm[C_AXIS] = dc * steps_to_mm[C_AXIS];
   #endif
-  delta_mm[E_AXIS] = esteps_float * steps_to_mm[E_AXIS_N];
+  delta_mm[E_AXIS] = esteps_float * steps_to_mm[E_AXIS_N(extruder)];
 
   if (block->steps[A_AXIS] < MIN_STEPS_PER_SEGMENT && block->steps[B_AXIS] < MIN_STEPS_PER_SEGMENT && block->steps[C_AXIS] < MIN_STEPS_PER_SEGMENT) {
     block->millimeters = ABS(delta_mm[E_AXIS]);
   #endif
   #if ENABLED(LIN_ADVANCE)
     if (block->use_advance_lead) {
-      block->advance_speed = (STEPPER_TIMER_RATE) / (extruder_advance_K[active_extruder] * block->e_D_ratio * block->acceleration * axis_steps_per_mm[E_AXIS_N]);
+      block->advance_speed = (STEPPER_TIMER_RATE) / (extruder_advance_K[active_extruder] * block->e_D_ratio * block->acceleration * axis_steps_per_mm[E_AXIS_N(extruder)]);
       #if ENABLED(LA_DEBUG)
         if (extruder_advance_K[active_extruder] * block->e_D_ratio * block->acceleration * 2 < SQRT(block->nominal_speed_sqr) * block->e_D_ratio)
           SERIAL_ECHOLNPGM("More than 2 steps per eISR loop executed.");
 
   // When changing extruders recalculate steps corresponding to the E position
   #if ENABLED(DISTINCT_E_FACTORS)
-    if (last_extruder != extruder && axis_steps_per_mm[E_AXIS_N] != axis_steps_per_mm[E_AXIS + last_extruder]) {
-      position[E_AXIS] = LROUND(position[E_AXIS] * axis_steps_per_mm[E_AXIS_N] * steps_to_mm[E_AXIS + last_extruder]);
+    if (last_extruder != extruder && axis_steps_per_mm[E_AXIS_N(extruder)] != axis_steps_per_mm[E_AXIS + last_extruder]) {
+      position[E_AXIS] = LROUND(position[E_AXIS] * axis_steps_per_mm[E_AXIS_N(extruder)] * steps_to_mm[E_AXIS + last_extruder]);
       last_extruder = extruder;
     }
   #endif
     LROUND(a * axis_steps_per_mm[A_AXIS]),
     LROUND(b * axis_steps_per_mm[B_AXIS]),
     LROUND(c * axis_steps_per_mm[C_AXIS]),
-    LROUND(e * axis_steps_per_mm[E_AXIS_N])
+    LROUND(e * axis_steps_per_mm[E_AXIS_N(extruder)])
   };
 
   #if HAS_POSITION_FLOAT

Marlin/src/module/stepper_indirection.cpp

     _TMC_INIT(Z3, planner.axis_steps_per_mm[Z_AXIS]);
   #endif
   #if AXIS_IS_TMC(E0)
-    _TMC_INIT(E0, planner.axis_steps_per_mm[E_AXIS]);
+    _TMC_INIT(E0, planner.axis_steps_per_mm[E_AXIS_N(0)]);
   #endif
   #if AXIS_IS_TMC(E1)
-    { constexpr uint8_t extruder = 1; _TMC_INIT(E1, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }
+    _TMC_INIT(E1, planner.axis_steps_per_mm[E_AXIS_N(1)]);
   #endif
   #if AXIS_IS_TMC(E2)
-    { constexpr uint8_t extruder = 2; _TMC_INIT(E2, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }
+    _TMC_INIT(E2, planner.axis_steps_per_mm[E_AXIS_N(2)]);
   #endif
   #if AXIS_IS_TMC(E3)
-    { constexpr uint8_t extruder = 3; _TMC_INIT(E3, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }
+    _TMC_INIT(E3, planner.axis_steps_per_mm[E_AXIS_N(3)]);
   #endif
   #if AXIS_IS_TMC(E4)
-    { constexpr uint8_t extruder = 4; _TMC_INIT(E4, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }
+    _TMC_INIT(E4, planner.axis_steps_per_mm[E_AXIS_N(4)]);
   #endif
   #if AXIS_IS_TMC(E5)
-    { constexpr uint8_t extruder = 5; _TMC_INIT(E5, planner.axis_steps_per_mm[E_AXIS_N]); UNUSED(extruder); }
+    _TMC_INIT(E5, planner.axis_steps_per_mm[E_AXIS_N(5)]);
   #endif
 
   #if USE_SENSORLESS