Split the software endstop capability by axis.

Based on #7975 and #7979

Marlin/Configuration.h

 #define Y_MAX_POS Y_BED_SIZE
 #define Z_MAX_POS 200
 
-// If enabled, axes won't move below MIN_POS in response to movement commands.
+/**
+ * Software Endstops
+ *
+ * - Prevent moves outside the set machine bounds.
+ * - Individual axes can be disabled, if desired.
+ * - X and Y only apply to Cartesian robots.
+ * - Use 'M211' to set software endstops on/off or report current state
+ */
+
+// Min software endstops curtail movement below minimum coordinate bounds
 #define MIN_SOFTWARE_ENDSTOPS
-// If enabled, axes won't move above MAX_POS in response to movement commands.
+#if ENABLED(MIN_SOFTWARE_ENDSTOPS)
+  #define MIN_SOFTWARE_ENDSTOP_X
+  #define MIN_SOFTWARE_ENDSTOP_Y
+  #define MIN_SOFTWARE_ENDSTOP_Z
+#endif
+
+// Max software endstops curtail movement above maximum coordinate bounds
 #define MAX_SOFTWARE_ENDSTOPS
+#if ENABLED(MAX_SOFTWARE_ENDSTOPS)
+  #define MAX_SOFTWARE_ENDSTOP_X
+  #define MAX_SOFTWARE_ENDSTOP_Y
+  #define MAX_SOFTWARE_ENDSTOP_Z
+#endif
 
 /**
  * Filament Runout Sensor

Marlin/Marlin_main.cpp

    * Constrain the given coordinates to the software endstops.
    */
 
-  // NOTE: This makes no sense for delta beds other than Z-axis.
-  //       For delta the X/Y would need to be clamped at
-  //       DELTA_PRINTABLE_RADIUS from center of bed, but delta
-  //       now enforces is_position_reachable for X/Y regardless
-  //       of HAS_SOFTWARE_ENDSTOPS, so that enforcement would be
-  //       redundant here.
-
+  /**
+   * Constrain the given coordinates to the software endstops.
+   *
+   * NOTE: This will only apply to Z on DELTA and SCARA. XY is
+   *       constrained to a circle on these kinematic systems.
+   */
   void clamp_to_software_endstops(float target[XYZ]) {
     if (!soft_endstops_enabled) return;
-    #if ENABLED(MIN_SOFTWARE_ENDSTOPS)
-      #if DISABLED(DELTA)
-        NOLESS(target[X_AXIS], soft_endstop_min[X_AXIS]);
-        NOLESS(target[Y_AXIS], soft_endstop_min[Y_AXIS]);
-      #endif
+    #if ENABLED(MIN_SOFTWARE_ENDSTOP_X)
+      NOLESS(target[X_AXIS], soft_endstop_min[X_AXIS]);
+    #endif
+    #if ENABLED(MIN_SOFTWARE_ENDSTOP_Y)
+      NOLESS(target[Y_AXIS], soft_endstop_min[Y_AXIS]);
+    #endif
+    #if ENABLED(MIN_SOFTWARE_ENDSTOP_Z)
       NOLESS(target[Z_AXIS], soft_endstop_min[Z_AXIS]);
     #endif
-    #if ENABLED(MAX_SOFTWARE_ENDSTOPS)
-      #if DISABLED(DELTA)
-        NOMORE(target[X_AXIS], soft_endstop_max[X_AXIS]);
-        NOMORE(target[Y_AXIS], soft_endstop_max[Y_AXIS]);
-      #endif
+    #if ENABLED(MAX_SOFTWARE_ENDSTOP_X)
+      NOMORE(target[X_AXIS], soft_endstop_max[X_AXIS]);
+    #endif
+    #if ENABLED(MAX_SOFTWARE_ENDSTOP_Y)
+      NOMORE(target[Y_AXIS], soft_endstop_max[Y_AXIS]);
+    #endif
+    #if ENABLED(MAX_SOFTWARE_ENDSTOP_Z)
       NOMORE(target[Z_AXIS], soft_endstop_max[Z_AXIS]);
     #endif
   }

Marlin/SanityCheck.h

   "Movement bounds ([XY]_MIN_POS, [XY]_MAX_POS) are too narrow to contain [XY]_BED_SIZE.");
 
 /**
+ * Granular software endstops (Marlin >= 1.1.7)
+ */
+#if ENABLED(MIN_SOFTWARE_ENDSTOPS) && DISABLED(MIN_SOFTWARE_ENDSTOP_Z)
+  #if IS_KINEMATIC
+    #error "MIN_SOFTWARE_ENDSTOPS on DELTA/SCARA also requires MIN_SOFTWARE_ENDSTOP_Z."
+  #elif DISABLED(MIN_SOFTWARE_ENDSTOP_X) && DISABLED(MIN_SOFTWARE_ENDSTOP_Y)
+    #error "MIN_SOFTWARE_ENDSTOPS requires at least one of the MIN_SOFTWARE_ENDSTOP_[XYZ] options."
+  #endif
+#endif
+
+#if ENABLED(MAX_SOFTWARE_ENDSTOPS) && DISABLED(MAX_SOFTWARE_ENDSTOP_Z)
+  #if IS_KINEMATIC
+    #error "MAX_SOFTWARE_ENDSTOPS on DELTA/SCARA also requires MAX_SOFTWARE_ENDSTOP_Z."
+  #elif DISABLED(MAX_SOFTWARE_ENDSTOP_X) && DISABLED(MAX_SOFTWARE_ENDSTOP_Y)
+    #error "MAX_SOFTWARE_ENDSTOPS requires at least one of the MAX_SOFTWARE_ENDSTOP_[XYZ] options."
+  #endif
+#endif
+
+/**
  * Progress Bar
  */
 #if ENABLED(LCD_PROGRESS_BAR)

Marlin/ultralcd.cpp

       float min = current_position[axis] - 1000,
             max = current_position[axis] + 1000;
 
-      #if HAS_SOFTWARE_ENDSTOPS
-        // Limit to software endstops, if enabled
-        if (soft_endstops_enabled) {
-          #if ENABLED(MIN_SOFTWARE_ENDSTOPS)
-            min = soft_endstop_min[axis];
-          #endif
-          #if ENABLED(MAX_SOFTWARE_ENDSTOPS)
-            max = soft_endstop_max[axis];
-          #endif
+      // Limit to software endstops, if enabled
+      #if ENABLED(MIN_SOFTWARE_ENDSTOPS) || ENABLED(MAX_SOFTWARE_ENDSTOPS)
+        if (soft_endstops_enabled) switch (axis) {
+          case X_AXIS:
+            #if ENABLED(MIN_SOFTWARE_ENDSTOP_X)
+              min = soft_endstop_min[X_AXIS];
+            #endif
+            #if ENABLED(MAX_SOFTWARE_ENDSTOP_X)
+              max = soft_endstop_max[X_AXIS];
+            #endif
+            break;
+          case Y_AXIS:
+            #if ENABLED(MIN_SOFTWARE_ENDSTOP_Y)
+              min = soft_endstop_min[Y_AXIS];
+            #endif
+            #if ENABLED(MAX_SOFTWARE_ENDSTOP_Y)
+              max = soft_endstop_max[Y_AXIS];
+            #endif
+            break;
+          case Z_AXIS:
+            #if ENABLED(MIN_SOFTWARE_ENDSTOP_Z)
+              min = soft_endstop_min[Z_AXIS];
+            #endif
+            #if ENABLED(MAX_SOFTWARE_ENDSTOP_Z)
+              max = soft_endstop_max[Z_AXIS];
+            #endif
+            break;
         }
-      #endif
+      #endif // MIN_SOFTWARE_ENDSTOPS || MAX_SOFTWARE_ENDSTOPS
 
       // Delta limits XY based on the current offset from center
       // This assumes the center is 0,0