Fix: guard all QSPI code with #if CIRCUITPY_QSPIBUS to eliminate non-QSPI build impact

Three issues found and fixed:

1. bus_core.c: displayio_display_bus_send_region_commands() was compiled
   unconditionally, adding ~110 lines of dead code to every non-QSPI
   display build. Now guarded with #if CIRCUITPY_QSPIBUS.

2. bus_core.h: Same guard for the declaration.

3. BusDisplay.c: The previous commit moved set_region_to_update() after
   fill_area() even for non-QSPI buses, changing the call ordering.
   Now the non-QSPI else-block reproduces the exact original ordering:
   set_region_to_update → size_calc → fill_area → is_free → send_pixels.

Verified: when CIRCUITPY_QSPIBUS=0, all C statements in the affected
files are identical to the original codebase.

Co-authored-by: ppsx <7107135+ppsx@users.noreply.github.com>

Author: Copilot

shared-module/busdisplay/BusDisplay.c

@@ -325,33 +325,42 @@ static bool _refresh_area(busdisplay_busdisplay_obj_t *self, const displayio_are
         }
         remaining_rows -= rows_per_buffer;
 
-        uint16_t subrectangle_size_bytes;
-        if (self->core.colorspace.depth >= 8) {
-            subrectangle_size_bytes = displayio_area_size(&subrectangle) * (self->core.colorspace.depth / 8);
-        } else {
-            subrectangle_size_bytes = displayio_area_size(&subrectangle) / (8 / self->core.colorspace.depth);
-        }
+        #if CIRCUITPY_QSPIBUS
+        if (is_qspi_bus) {
+            // QSPI path: fill_area first (overlaps with previous DMA),
+            // then single-transaction set_region + RAMWR + pixels.
+            // depth is always 16 here (guarded by is_qspi_bus check above).
+            uint16_t subrectangle_size_bytes = displayio_area_size(&subrectangle) * (self->core.colorspace.depth / 8);
 
-        memset(mask, 0, mask_length * sizeof(mask[0]));
-        memset(buffer, 0, buffer_size * sizeof(buffer[0]));
+            memset(mask, 0, mask_length * sizeof(mask[0]));
+            memset(buffer, 0, buffer_size * sizeof(buffer[0]));
 
-        displayio_display_core_fill_area(&self->core, &subrectangle, mask, buffer);
+            displayio_display_core_fill_area(&self->core, &subrectangle, mask, buffer);
 
-        #if CIRCUITPY_QSPIBUS
-        if (is_qspi_bus) {
-            // QSPI single-transaction path: set_region + RAMWR + pixels
-            // in one begin/end, eliminating per-subrectangle transaction
-            // overhead. begin_transaction waits for any prior async DMA
-            // to finish, so fill_area above overlaps with previous DMA.
+            // begin_transaction waits for any prior async DMA to finish,
+            // so fill_area above overlaps with previous DMA.
             displayio_display_bus_begin_transaction(&self->bus);
             displayio_display_bus_send_region_commands(&self->bus, &self->core, &subrectangle);
             _send_pixels(self, (uint8_t *)buffer, subrectangle_size_bytes);
             displayio_display_bus_end_transaction(&self->bus);
         } else
         #endif
         {
+            // Non-QSPI path: original ordering preserved exactly.
             displayio_display_bus_set_region_to_update(&self->bus, &self->core, &subrectangle);
 
+            uint16_t subrectangle_size_bytes;
+            if (self->core.colorspace.depth >= 8) {
+                subrectangle_size_bytes = displayio_area_size(&subrectangle) * (self->core.colorspace.depth / 8);
+            } else {
+                subrectangle_size_bytes = displayio_area_size(&subrectangle) / (8 / self->core.colorspace.depth);
+            }
+
+            memset(mask, 0, mask_length * sizeof(mask[0]));
+            memset(buffer, 0, buffer_size * sizeof(buffer[0]));
+
+            displayio_display_core_fill_area(&self->core, &subrectangle, mask, buffer);
+
             // Can't acquire display bus; skip the rest of the data.
             if (!displayio_display_bus_is_free(&self->bus)) {
                 return false;

shared-module/displayio/bus_core.c

@@ -101,6 +101,7 @@ void displayio_display_bus_end_transaction(displayio_display_bus_t *self) {
     self->end_transaction(self->bus);
 }
 
+#if CIRCUITPY_QSPIBUS
 // Send column/row window commands. Caller must already be in a transaction.
 void displayio_display_bus_send_region_commands(displayio_display_bus_t *self, displayio_display_core_t *display, displayio_area_t *area) {
     uint16_t x1 = area->x1 + self->colstart;
@@ -210,6 +211,7 @@ void displayio_display_bus_send_region_commands(displayio_display_bus_t *self, d
         self->send(self->bus, DISPLAY_DATA, chip_select, data, data_length / 2);
     }
 }
+#endif
 
 void displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, displayio_display_core_t *display, displayio_area_t *area) {
     uint16_t x1 = area->x1 + self->colstart;

shared-module/displayio/bus_core.h

@@ -49,9 +49,11 @@ void displayio_display_bus_end_transaction(displayio_display_bus_t *self);
 
 void displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, displayio_display_core_t *display, displayio_area_t *area);
 
+#if CIRCUITPY_QSPIBUS
 // Send column/row window commands within an already-open transaction.
 // Caller must have called displayio_display_bus_begin_transaction() first.
 void displayio_display_bus_send_region_commands(displayio_display_bus_t *self, displayio_display_core_t *display, displayio_area_t *area);
+#endif
 
 void release_display_bus(displayio_display_bus_t *self);