nRF52840 + SSD1680 (mipi-dbi-spi) + LVGL

Question

Hi,

I'm working on a custom board based on nRF52840 and a 2.9" ePaper display (SSD1680) connected via SPI using the mipi-dbi-spi interface.
I'm using nRF Connect SDK v3.0.0 (Zephyr) and LVGL for graphics rendering.

In the devicetree, the display is marked with zephyr,deferred-init because I only power the display later from main():

.overlay:

&spi1 {
    compatible = "nordic,nrf-spi";
    status = "okay";
    cs-gpios = <&gpio0 22 GPIO_ACTIVE_LOW>;
    pinctrl-0 = <&spi1_default>;
    pinctrl-1 = <&spi1_sleep>;
    pinctrl-names = "default", "sleep";
};
&spi1_default {
    group1 {
        psels = <NRF_PSEL(SPIM_SCK, 0, 20)>,
                <NRF_PSEL(SPIM_MOSI, 0, 17)>; //SDA
                // <NRF_PSEL(SPIM_MISO, 0, 8)>;
    };
};

&spi1_sleep {
    group1 {
        psels = <NRF_PSEL(SPIM_SCK, 0, 20)>,
                <NRF_PSEL(SPIM_MOSI, 0, 17)>; //SDA
                // <NRF_PSEL(SPIM_MISO, 0, 8)>;
    };
};

/ {
    mipi_dbi_waveshare_epaper_gdeh029a1 {
        compatible = "zephyr,mipi-dbi-spi";
        spi-dev = <&spi1>;
        dc-gpios = <&gpio0 24 GPIO_ACTIVE_HIGH>;
        reset-gpios = <&gpio1 0 GPIO_ACTIVE_LOW>;

        #address-cells = <1>;
        #size-cells = <0>;
        // write-only;

        ssd16xx_waveshare_epaper_gdeh029a1: ssd16xxfb@0 {
            compatible = "gooddisplay,gdey0213b74", "solomon,ssd1680";
            mipi-max-frequency = <1000000>;
            reg = <0>;
            width = <296>;
            height = <128>;
            busy-gpios = <&gpio0 11 GPIO_ACTIVE_HIGH>;

            tssv = <0x80>;
            zephyr,deferred-init;

            full {
                border-waveform = <0x05>;
            };

            partial {
                border-waveform = <0x3c>;
            };
        };
    };
};


/ {
    chosen {
        nvs-storage = &storage_partition;
        zephyr,console = &cdc_acm_uart0;
        zephyr,display = &ssd16xx_waveshare_epaper_gdeh029a1;
    };
};

prj.conf:

CONFIG_DISPLAY=y
CONFIG_SSD16XX=y

# Enable SPI
CONFIG_SPI=y
CONFIG_SPI_NRFX=y

CONFIG_MAIN_STACK_SIZE=16384
CONFIG_HEAP_MEM_POOL_SIZE=2048


CONFIG_LVGL=y
CONFIG_LV_Z_MEM_POOL_SIZE=16384
CONFIG_LV_Z_AUTO_INIT=n
CONFIG_LV_USE_LOG=y
CONFIG_LV_USE_LABEL=y
CONFIG_LV_COLOR_DEPTH_1=y
CONFIG_LV_USE_LABEL=y
CONFIG_LV_LOG_LEVEL_TRACE=y
CONFIG_LV_Z_SHELL=y
CONFIG_LV_USE_MONKEY=y
CONFIG_LV_FONT_MONTSERRAT_14=y

K_THREAD_STACK_DEFINE(lvgl_stack_area, 32768);
static struct k_thread lvgl_stack_data;

static lv_obj_t *hello_world_label;
static const struct device *display_dev;

void view_lvgl()
{

	gpio_pin_set_dt(&out, 1);
	k_msleep(1000);

	display_dev = DEVICE_DT_GET(DT_CHOSEN(zephyr_display));
	device_init(display_dev);

	while (!device_is_ready(display_dev))
	{
		printk("Device not ready");
		k_msleep(100);
	}

	hello_world_label = lv_label_create(lv_scr_act());
	lv_label_set_text(hello_world_label, "Hello world!");
	lv_obj_align(hello_world_label, LV_ALIGN_CENTER, 0, 0);

	lv_task_handler();
	display_blanking_off(display_dev);

	while (1)
	{
		lv_task_handler();
		printk("view_lvgl loop\n");
		k_msleep(1000);
	}
}

However, after calling:

hello_world_label = lv_label_create(lv_scr_act());

I get a NULL pointer, and any further use causes a crash (lv_scr_act() returns NULL, and lv_label_create() returns NULL).

I assume this happens because no LVGL display was registered, due to the deferred init.

If I remove zephyr,deferred-init, then the display is not initialized at all.

Now I see fast blinking and part of the screen is filled with garbage when initializing.

Here is the initialization after power is applied.

How should I trigger full LVGL registration after enabling the display device at runtime?
Can I manually re-init the display driver (e.g., force call lv_disp_drv_register() or trigger the driver init() after power is applied)?
Is there a known working method to combine zephyr,deferred-init + LVGL for late-powered displays (e.g., ePaper)?

Any advice would be very helpful. Thank you in advance!

*** Booting nRF Connect SDK v3.0.2-89ba1294ac9b ***
*** Using Zephyr OS v4.0.99-f791c49f492c ***
[00:00:00.002,868] [1;31m<err> lvgl: Display device not ready.[0m
USB CDC ready. Type something...
[00:00:00.108,947] [0m<inf> fs_nvs: 8 Sectors of 4096 bytes[0m
[00:00:00.108,947] [0m<inf> fs_nvs: alloc wra: 0, f30[0m
[00:00:00.108,947] [0m<inf> fs_nvs: data wra: 0, 2c8[0m
[00:00:00.109,344] [0m<inf> bt_sdc_hci_driver: SoftDevice Controller build revision: 
                                            89 9a 50 8a 95 01 9c 58  fc 39 d2 c1 10 04 ee 02 |..P....X .9......
                                            64 ce 25 be                                      |d.%.             [0m
[00:00:00.112,121] [0m<inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)[0m
[00:00:00.112,152] [0m<inf> bt_hci_core: HW Variant: nRF52x (0x0002)[0m
[00:00:00.112,182] [0m<inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 137.20634 Build 2617349514[0m
[00:00:00.112,426] [0m<i
view_lvgl loop

nRF52840 + SSD1680 (mipi-dbi-spi) + LVGL

My questions: