Fix display bus transaction handling.

Fixes #10569

Author: JamesWhitlock

shared-module/busdisplay/BusDisplay.c

@@ -273,7 +273,10 @@ static bool _refresh_area(busdisplay_busdisplay_obj_t *self, const displayio_are
         }
         remaining_rows -= rows_per_buffer;
 
-        displayio_display_bus_set_region_to_update(&self->bus, &self->core, &subrectangle);
+        if (!displayio_display_bus_set_region_to_update(&self->bus, &self->core, &subrectangle)) {
+            // This is a failure to acquire the bus, skip the rest of the refresh.
+            return false;
+        }
 
         uint16_t subrectangle_size_bytes;
         if (self->core.colorspace.depth >= 8) {
@@ -287,12 +290,11 @@ static bool _refresh_area(busdisplay_busdisplay_obj_t *self, const displayio_are
 
         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)) {
+        // If we can't acquire display bus; skip the rest of the data.
+        if (!displayio_display_bus_begin_transaction(&self->bus)) {
             return false;
         }
 
-        displayio_display_bus_begin_transaction(&self->bus);
         _send_pixels(self, (uint8_t *)buffer, subrectangle_size_bytes);
         displayio_display_bus_end_transaction(&self->bus);
 
@@ -310,7 +312,7 @@ static bool _refresh_area(busdisplay_busdisplay_obj_t *self, const displayio_are
 
 static void _refresh_display(busdisplay_busdisplay_obj_t *self) {
     if (!displayio_display_bus_is_free(&self->bus)) {
-        // A refresh on this bus is already in progress.  Try next display.
+        // Don't bother with the refresh if the bus is already busy
         return;
     }
     displayio_display_core_start_refresh(&self->core);

shared-module/displayio/bus_core.c

@@ -101,7 +101,8 @@ void displayio_display_bus_end_transaction(displayio_display_bus_t *self) {
     self->end_transaction(self->bus);
 }
 
-void displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, displayio_display_core_t *display, displayio_area_t *area) {
+// Determine if this is run from a background task or not. Should we skip sending the data or wait for the bus?
+bool 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;
     uint16_t x2 = area->x2 + self->colstart;
     uint16_t y1 = area->y1 + self->rowstart;
@@ -127,8 +128,12 @@ void displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, d
         chip_select = CHIP_SELECT_TOGGLE_EVERY_BYTE;
     }
 
+    if (!displayio_display_bus_begin_transaction(self)) {
+        // Can't acquire display bus; skip and report failure.
+        return false;
+    }
+
     // Set column.
-    displayio_display_bus_begin_transaction(self);
     uint8_t data[5];
     data[0] = self->column_command;
     uint8_t data_length = 1;
@@ -163,20 +168,16 @@ void displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, d
     }
 
     self->send(self->bus, data_type, chip_select, data, data_length);
-    displayio_display_bus_end_transaction(self);
 
     if (self->set_current_column_command != NO_COMMAND) {
         uint8_t command = self->set_current_column_command;
-        displayio_display_bus_begin_transaction(self);
         self->send(self->bus, DISPLAY_COMMAND, chip_select, &command, 1);
         // Only send the first half of data because it is the first coordinate.
         self->send(self->bus, DISPLAY_DATA, chip_select, data, data_length / 2);
-        displayio_display_bus_end_transaction(self);
     }
 
 
     // Set row.
-    displayio_display_bus_begin_transaction(self);
     data[0] = self->row_command;
     data_length = 1;
     if (!self->data_as_commands) {
@@ -207,16 +208,15 @@ void displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, d
     }
 
     self->send(self->bus, data_type, chip_select, data, data_length);
-    displayio_display_bus_end_transaction(self);
 
     if (self->set_current_row_command != NO_COMMAND) {
         uint8_t command = self->set_current_row_command;
-        displayio_display_bus_begin_transaction(self);
         self->send(self->bus, DISPLAY_COMMAND, chip_select, &command, 1);
         // Only send the first half of data because it is the first coordinate.
         self->send(self->bus, DISPLAY_DATA, chip_select, data, data_length / 2);
-        displayio_display_bus_end_transaction(self);
     }
+    displayio_display_bus_end_transaction(self);
+    return true;
 }
 
 void displayio_display_bus_collect_ptrs(displayio_display_bus_t *self) {

shared-module/displayio/bus_core.h

@@ -47,7 +47,7 @@ bool displayio_display_bus_is_free(displayio_display_bus_t *self);
 bool displayio_display_bus_begin_transaction(displayio_display_bus_t *self);
 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);
+bool displayio_display_bus_set_region_to_update(displayio_display_bus_t *self, displayio_display_core_t *display, displayio_area_t *area);
 
 void release_display_bus(displayio_display_bus_t *self);
 

shared-module/epaperdisplay/EPaperDisplay.c

@@ -162,7 +162,9 @@ static void send_command_sequence(epaperdisplay_epaperdisplay_obj_t *self,
             data_size = ((data_size & ~DELAY) << 8) + *(cmd + 2);
             data = cmd + 3;
         }
-        displayio_display_bus_begin_transaction(&self->bus);
+        while (!displayio_display_bus_begin_transaction(&self->bus)) {
+            RUN_BACKGROUND_TASKS;
+        }
         self->bus.send(self->bus.bus, DISPLAY_COMMAND, self->chip_select, cmd, 1);
         self->bus.send(self->bus.bus, DISPLAY_DATA, self->chip_select, data, data_size);
         displayio_display_bus_end_transaction(&self->bus);
@@ -310,14 +312,21 @@ static bool epaperdisplay_epaperdisplay_refresh_area(epaperdisplay_epaperdisplay
         uint16_t remaining_rows = displayio_area_height(&clipped);
 
         if (self->bus.row_command != NO_COMMAND) {
-            displayio_display_bus_set_region_to_update(&self->bus, &self->core, &clipped);
+            if (!displayio_display_bus_set_region_to_update(&self->bus, &self->core, &clipped)) {
+                // This is a failure to acquire the bus, skip the rest of the refresh.
+                return false;
+            }
         }
 
         uint8_t write_command = self->write_black_ram_command;
         if (pass == 1) {
             write_command = self->write_color_ram_command;
         }
-        displayio_display_bus_begin_transaction(&self->bus);
+
+        if (!displayio_display_bus_begin_transaction(&self->bus)) {
+            // We can't acquire the bus skip the rest of the refresh.
+            return false;
+        }
         self->bus.send(self->bus.bus, DISPLAY_COMMAND, self->chip_select, &write_command, 1);
         displayio_display_bus_end_transaction(&self->bus);
 
@@ -394,24 +403,26 @@ static bool _clean_area(epaperdisplay_epaperdisplay_obj_t *self) {
     memset(buffer, 0x77, width / 2);
 
     uint8_t write_command = self->write_black_ram_command;
-    displayio_display_bus_begin_transaction(&self->bus);
+
+    if (!displayio_display_bus_begin_transaction(&self->bus)) {
+        // Can't acquire display bus; skip the rest of the data. Try next display.
+        return false;
+    }
     self->bus.send(self->bus.bus, DISPLAY_COMMAND, self->chip_select, &write_command, 1);
-    displayio_display_bus_end_transaction(&self->bus);
 
     for (uint16_t j = 0; j < height; j++) {
-        if (!displayio_display_bus_begin_transaction(&self->bus)) {
-            // Can't acquire display bus; skip the rest of the data. Try next display.
-            return false;
-        }
         self->bus.send(self->bus.bus, DISPLAY_DATA, self->chip_select, buffer, width / 2);
-        displayio_display_bus_end_transaction(&self->bus);
 
         // TODO(tannewt): Make refresh displays faster so we don't starve other
         // background tasks.
         #if CIRCUITPY_TINYUSB
-        usb_background();
+        displayio_display_bus_end_transaction(&self->bus);
+        do {
+            usb_background();
+        } while (!displayio_display_bus_begin_transaction(&self->bus));
         #endif
     }
+    displayio_display_bus_end_transaction(&self->bus);
 
     return true;
 }