Device Tree To Support DDC/CI For HDMI On i.MX8

[kendalla59]

I have a small embedded HDMI display, and I would like to add some monitor controls into the user interface. The display supports DDC/CI but my i.MX8 device tree does not expose the i2c lines for the HDMI port. I've searched through the linux-imx/arch/arm64/boot/dts/freescale files, and I can't find any examples of this.

Can somebody please help me to get access to the dedicated SDA/SCL for the HDMI interface?

[darko31]

Hi we've had a similar problem with wanting to send commands over the DDC lines.

Take a look at the cdns_hdmi_scdc_write function.

https://github.com/nxp-imx/linux-imx/blob/lf-5.15.y/drivers/gpu/drm/bridge/cadence/cdns-mhdp-hdmi.c#...

It is possible create a custom function similar to the cdns_hdmi_scdc. The data can be hardcoded in the driver and called from initialization or via sysfs interface.

Just make sure to have the 0 and 1 in the message in the same way as in the cdns_hdmi_scdc_write function otherwise the packet isn't sent properly. I believe it's some kind of message protocol to the mailbox register of the HDMI IP but I'm not entirely sure.

Best regards,

Darko

[joanxie]

what imx8 processor do you use? imx8qm?

[kendalla59]

I'm using the i.MX 8M, I believe. It's a BCM AR8MXMQ board.

https://www.bcmcom.com/bcm_product_AR8MXMQ.html