hexwab
Posts: 1
Joined: Wed Oct 02, 2019 11:18 am

No HDMI hotplug detection with Full KMS on CM3

Fri Dec 13, 2019 7:17 pm

So I have a custom CM3 board based upon the reference devkit design. It outputs just fine over HDMI when in legacy or in fake KMS mode, but not in full KMS.

When in full KMS it thinks HDMI is disconnected and outputs over composite instead. If I write to /sys/class/drm/card0-HDMI-A-1/status I can force HDMI to be connected, after which HDMI output works (including DDC).

So this would seem to be a hotplug issue, specifically hotplug detection on the ARM, which makes me think devicetree.

I have tried setting "device_tree=$FILENAME" in /boot/cmdline.txt to both bcm2708-rpi-cm.dtb (the default apparently even for the CM3?) and bcm2710-rpi-cm3.dtb, although I note that https://github.com/raspberrypi/linux/bl ... 3.dts#L132 shows hotplug as being on pin 46 (as for the CM) instead of 128 (on the CM3). Is this correct?

Thanks,

Tom.

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: No HDMI hotplug detection with Full KMS on CM3

Fri Dec 13, 2019 10:34 pm

That does look incorrect, but you can't address it as GPIO 128 from Linux as you need to direct it to the correct GPIO controller driver.
I'd expect it to be

Code: Select all

hpd-gpios = <&expgpio 0 GPIO_ACTIVE_LOW>;
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