display: add display_flush

drivers/display/display_dummy.c

@@ -57,6 +57,11 @@ static int dummy_display_write(const struct device *dev, const uint16_t x,
 	return 0;
 }
 
+static int dummy_display_flush(const struct device *dev)
+{
+	return 0;
+}
+
 static int dummy_display_blanking_off(const struct device *dev)
 {
 	return 0;
@@ -110,6 +115,7 @@ static const struct display_driver_api dummy_display_api = {
 	.blanking_on = dummy_display_blanking_on,
 	.blanking_off = dummy_display_blanking_off,
 	.write = dummy_display_write,
+	.flush = dummy_display_flush,
 	.set_brightness = dummy_display_set_brightness,
 	.set_contrast = dummy_display_set_contrast,
 	.get_capabilities = dummy_display_get_capabilities,

include/zephyr/drivers/display.h

@@ -163,6 +163,13 @@ typedef int (*display_read_api)(const struct device *dev, const uint16_t x,
 				const struct display_buffer_descriptor *desc,
 				void *buf);
 
+/**
+ * @typedef display_flush_api
+ * @brief Callback API to indicate that all previous writes should be flushed to the display
+ * See display_flush() for argument description
+ */
+typedef int (*display_flush_api)(const struct device *dev);
+
 /**
  * @typedef display_get_framebuffer_api
  * @brief Callback API to get framebuffer pointer
@@ -222,6 +229,7 @@ __subsystem struct display_driver_api {
 	display_blanking_off_api blanking_off;
 	display_write_api write;
 	display_read_api read;
+	display_flush_api flush;
 	display_get_framebuffer_api get_framebuffer;
 	display_set_brightness_api set_brightness;
 	display_set_contrast_api set_contrast;
@@ -279,6 +287,27 @@ static inline int display_read(const struct device *dev, const uint16_t x,
 	return api->read(dev, x, y, desc, buf);
 }
 
+/**
+ * @brief Indicates that all previous writes should be flushed to the display
+ *
+ * Can be used to present all previous writes simultaneously, for
+ * double buffered or latched displays.
+ *
+ * @param dev Pointer to device structure
+ *
+ * @retval 0 on success else negative errno code.
+ */
+static inline int display_flush(const struct device *dev)
+{
+	struct display_driver_api *api = (struct display_driver_api *)dev->api;
+
+	if (api->flush == NULL) {
+		return -ENOSYS;
+	}
+
+	return api->flush(dev);
+}
+
 /**
  * @brief Get pointer to framebuffer for direct access
  *

modules/lvgl/Kconfig

@@ -102,6 +102,7 @@ config LV_Z_FLUSH_THREAD_STACK_SIZE
 	default 1024
 	help
 	  Stack size for LVGL flush thread, which will call display_write
+	  and display_flush
 
 config LV_Z_FLUSH_THREAD_PRIO
 	int "LVGL flush thread priority"

modules/lvgl/lvgl_display.c

@@ -24,12 +24,17 @@ void lvgl_flush_thread_entry(void *arg1, void *arg2, void *arg3)
 	while (1) {
 		k_msgq_get(&flush_queue, &flush, K_FOREVER);
 		data = (struct lvgl_disp_data *)flush.disp_drv->user_data;
+		const bool is_last = lv_disp_flush_is_last(flush.disp_drv);
 
 		display_write(data->display_dev, flush.x, flush.y, &flush.desc,
 			      flush.buf);
 
 		lv_disp_flush_ready(flush.disp_drv);
 		k_sem_give(&flush_complete);
+
+		if (is_last) {
+			display_flush(data->display_dev);
+		}
 	}
 }
 
@@ -129,11 +134,15 @@ void lvgl_flush_display(struct lvgl_display_flush *request)
 	k_yield();
 #else
 	/* Write directly to the display */
-	struct lvgl_disp_data *data =
-		(struct lvgl_disp_data *)request->disp_drv->user_data;
+	struct lvgl_disp_data *data = (struct lvgl_disp_data *)request->disp_drv->user_data;
+	const bool is_last = lv_disp_flush_is_last(request->disp_drv);
 
 	display_write(data->display_dev, request->x, request->y,
 		      &request->desc, request->buf);
 	lv_disp_flush_ready(request->disp_drv);
+
+	if (is_last) {
+		display_flush(data->display_dev);
+	}
 #endif
 }

modules/lvgl/lvgl_display_mono.c

@@ -48,6 +48,10 @@ void lvgl_flush_cb_mono(lv_disp_drv_t *disp_drv, const lv_area_t *area, lv_color
 	}
 
 	lv_disp_flush_ready(disp_drv);
+
+	if (is_last) {
+		display_flush(display_dev);
+	}
 }
 
 void lvgl_set_px_cb_mono(lv_disp_drv_t *disp_drv, uint8_t *buf, lv_coord_t buf_w, lv_coord_t x,