Before I start debugging, I have a quick question: Is the current RPi3 system (v1.28.1) supposed to display a console on the RPi 7" Touchscreen? Raspbian uses the screen without any problem, so the screen is fine.
I flashed a new barebones Nerves (v1.10) app, but the screen remains black. It seems like not even the backlight turns on. However, the screen itself is detected by Linux. I can even set the brightness in /sys/ without any effect, though.
Do you have any pointers on how to address this issue?
I’m giving up for now. I tried a whole lot of different config.txt/cmdline.txt settings without any success. The only thing remaining might be the Linux kernel version, which might explain why it did work out of the box previously (2 years ago). I’m not going down this route for now, however.
The strange thing is that according to dmesg, the display itself, framebuffer (at the correct size), and even touchscreen are detected … it’s just black (regardless of the brightness and bl_power settings).
@udoschneider have you tried any 1.27.x or 1.26.x rpi3 system versions? Helping narrow down where the behavior change is could be helpful if able. It will be a bit before I’m around a 7” screen again to play around with this, but I believe the default was to show the console
Forcing nerves to use a 1.27.1 system shows the console on the touchscreen as expected. I noticed though, that this also requires a downgrade to OTP26 (26.2.5.3 in my case).
PASS: erlang 26.2.5.3, elixir 1.17.3-otp-26 and nerves_system_rpi3 1.27.1
FAIL: erlang 27.0.1, elixir 1.17.2-otp-27 and nerves_system_rpi3 1.28.1 (Erlang/Elixir version from the nerves install docs)
FAIL: erlang 27.1.1, elixir 1.17.3-otp-27 and nerves_system_rpi3 1.28.1 (Erlang/Elixir version updated)
I’m not sure if it’s the system update or the OTP update. Unfortunately, as far as I can see, the systems are bound to the OTP version. So, simply changing one without changing the other (which might make deciding which is the “culprit” easier) is not possible.
The display stops working between commits 1712c7c6ea4ed0ece8a560a6daf7087d5b86f70c "Only trim serial number for hostname" and e0c89818e4192b469a502ee7e9cb480756ffef16 "Update to Linux 6.6, DRM, and libcamera".
The most obvious culprit is a linux defconfig change with the working commit having CONFIG_FRAMEBUFFER_CONSOLE=y set and the later commit having this option removed.
I’ll build a new custom system based on 1.8.1 with this option set tomorrow to verify.
I’m still wondering, though, if this change was intentional. From my understanding, this should also apply to HDMI output.
Switch from the Raspberry Pi’s deprecated MMAL media support to DRM and libcamera. This is a big change if you use the display or camera that has been a long time coming. Please plan some time to make the upgrade.
In theory, you could backport the OTP 27 update to the nerves_system_rpi3 v1.27.1. It’s not that complicated, but not worth the time.
Could you create an issue to track the console for the touchscreen?
I took a quick look. I only use the RPi3 headless, but if I were to take a first guess, I’d modify the config.txt (just manually do it by mounting the boot partition of the MicroSD card on your build machine) and add this:
# Automatically load overlays for detected DSI displays
display_auto_detect=1
and also copy vc4-kms-dsi-7inch.dtbo into the overlays directory. It’s probably going to take a couple iterations and starting a GitHub issue seems like a better place to iterate. If that doesn’t work, try copying all of the dtbo files into the overlays directory. If that doesn’t work, then I’d run Raspberry Pi OS and run lsmod to see what kernel drivers are loaded and then run lsmod on Nerves and compare. It won’t be the same, but I’d expect a difference in vc4 drivers.
Sorry to give so many instructions. I think a lot of the Nerves core team is traveling or prepping for travel right now with out Raspberry Pi 3’s on hand. It definitely looks like something was missed on the big MMAL->DRM update for RPi3, though.
