Need Help Enabling HDMI on Debix Model A

[Laurent Pinchart]

Hi Tarang,

On Mon, Apr 07, 2025 at 02:06:35PM +0000, Tarang Raval wrote:
> > On Mon, Apr 07, 2025 at 11:10:23AM +0000, Tarang Raval wrote:
> > > Hi Laurent,
> > >
> > > I’m trying to bring up HDMI on the Debix Model A board using the
> > > mainline kernel, but I’m currently facing issues.
> > >
> > > I saw that you tested the patch for HDMI support on this board in
> > > mainline, so I am hoping you could help me figure out what might be
> > > missing.
> > >
> > > To clarify — I'm using the prebuilt image provided by Debix, but I replaced
> > > the kernel image and the device tree (DTS) file in the /boot directory with
> > > ones built from the mainline kernel.
> > >
> > > I’ve enabled the following configurations in the kernel:
> > > CONFIG_DRM_DISPLAY_CONNECTOR=y
> > > CONFIG_DRM_IMX8MP_DW_HDMI_BRIDGE=y
> > > CONFIG_DRM_IMX8MP_HDMI_PVI=y
> > > CONFIG_DRM_IMX_LCDIF=y
> > > CONFIG_PHY_FSL_SAMSUNG_HDMI_PHY=y
> > >
> > > When I boot the board, I see the following HDMI/DRM related logs:
> > > debix at imx8mp-debix:~$ dmesg | grep -iE "drm|hdmi"
> > > [    0.121979] /soc at 0/bus at 32c00000/display-bridge at 32fc4000: Fixed dependency cycle(s) with /soc at 0/bus at 32c00000/hdmi at 32fd8000
> > > [    0.122164] /soc at 0/bus at 32c00000/hdmi at 32fd8000: Fixed dependency cycle(s) with /soc at 0/bus at 32c00000/display-bridge at 32fc4000
> > > [    0.127417] /soc at 0/bus at 32c00000/hdmi at 32fd8000: Fixed dependency cycle(s) with /hdmi-connector
> > > [    0.127608] /hdmi-connector: Fixed dependency cycle(s) with /soc at 0/bus at 32c00000/hdmi at 32fd8000
> > > [    1.947962] imx8mp-dw-hdmi-tx 32fd8000.hdmi: Detected HDMI TX controller v2.13a with HDCP (SAMSUNG HDMI TX PHY)
> > > [    1.949220] imx8mp-dw-hdmi-tx 32fd8000.hdmi: registered DesignWare HDMI I2C bus driver
> > > [    1.956365] [drm] Initialized imx-lcdif 1.0.0 for 32fc6000.display-controller on minor 0
> > > [    2.016601] imx-lcdif 32fc6000.display-controller: [drm] fb0: imx-lcdifdrmfb frame buffer device
> > > [    8.380915] systemd[1]: Starting Load Kernel Module drm...
> > >
> > >
> > > I also checked that the display's modeline is recognized under sysfs :
> > >
> > > root at imx8mp-debix:~# ls /sys/class/drm/card0-HDMI-A-1/
> > > connector_id  dpms          modes         subsystem/
> > > ddc/          edid          power/        uevent
> > > device/       enabled       status
> > >
> > > However, there is still no HDMI output on the display. Instead,
> > > I only see a white blinking cursor on the screen.. I'm not sure
> > > what I'm missing.
> > 
> > The white blinking cursor means the display is working from the kernel
> > point of view. What are you expecting, are you running an X server or
> > Wayland compositor ?
> 
> I'm expecting to see the Ubuntu desktop environment on the HDMI 
> display — just like how it appears with the original prebuilt image provided 
> by Debix. I'm running the default Ubuntu 22.04 LTS prebuilt image, and I only
> replaced the Image and .dtb file
> 
> I'm not explicitly launching an X server or Wayland compositor myself
> 
> However, based on your response, I now realize that I may also need to 
> enable GPU support in the mainline device tree. Specifically, I believe I 
> need to enable the gpu2D and gpu3D nodes to allow the graphical 
> environment to start properly and render the desktop over HDMI.
> 
> Does that sound correct, or is there anything else I should check or 
> enable?

That's a plausible explanation. The 2D GPU is probably not used by the
compositor, but a 3D GPU could be required. I'd recommend checking the
system logs to see why the compositor (or session manager) failed to
start.

> > > Could you please help me out or point me in the right direction?
> > >
> > > Thank you for your time.

-- 
Regards,

Laurent Pinchart