Support for Direct Framebuffer Write to Display on i.MX8QXP

[Ram2]

Hi NXP Team,

Soc : iMX8qxpC0mek
Linux O.S : yocto [Scarthgap L6.6.5 ]
We would like to check whether direct framebuffer writing to the display is supported on the i.MX8QXP Yocto Linux platform.

Our requirement is to display graphics or an image directly during the early boot stage, before the Weston/Wayland compositor and HMI application are initialized.

Could you please clarify:

1. Whether direct framebuffer access, such as /dev/fb0, is supported.
2. Whether the display can be updated directly using DRM/KMS without starting Weston.
3. Whether NXP provides any reference application or sample code for direct display rendering
4. The required kernel configurations, device-tree changes, or display-driver settings.
5. Whether direct framebuffer access could conflict with Weston when the compositor starts later.

Please share the recommended approach for implementing early display output on the i.MX8QXP platform.

[Manuel_Salas]

Hello @Ram2 

Hope you are doing very well.

1. Is /dev/fb0 (fbdev) supported?

No, not natively on i.MX 8. The NXP i.MX Linux Reference Manual explicitly shows ins chapter 6.2.2 Frame buffer:

Frame buffer drivers are supported for i.MX 6 and i.MX 7, but not for i.MX 8

2. Direct DRM/KMS access without Weston

Yes, this is the correct and supported approach.

On i.MX 8, Weston uses the DRM backend, which means Weston must not be running when an application directly accesses DRM/KMS. 

You can take a look to the chapter 7.3.10.7 cam test application of UG10163.

3. NXP Reference Application / Sample Code

You can take a look to the SDK_2_9_0_MEK-MIMX8QX\boards\mekmimx8qx\driver_examples\dpu\character example. Download it from MCUXpresso SDK.

4. Kernel Configuration, Device Tree, and Display Driver Settings

Kernel configuration (in imx_v8_defconfig):

CONFIG_DRM=y # DRM framework
CONFIG_DRM_IMX=y # i.MX DPU DRM driver (drivers/gpu/drm/imx)
CONFIG_DRM_IMX_DPU=y # DPU-specific DRM module
CONFIG_DRM_IMX_MIPI_DSI_NORTHWEST=y # MIPI DSI (for OLED panel support)
CONFIG_DRM_IMX_LDB=y # LVDS Display Bridge

Please take a look to the Table 10. Kernel and device tree configurations of RN00210, in section Video Display.

5. Conflict with Weston When It Starts Later

Yes, there is a conflict.

Since both the early-boot DRM/KMS application and Weston fight for exclusive control of /dev/dri/card0, the early application must release the DRM master before Weston starts.

You can try display via U-Boot logo. U-Boot supports BMP images rendered via DRM/simplefb. This completely avoids the Linux-layer conflict and produces the earliest possible splash screen.

Best regards,

Salas.