Thursday, March 3, 2022

[fedora-arm] Re: Change in kernel PPS GPIO handling?

I poked at this some more tonight, starting with a fresh SD card install
of F35. This is in a Pi 4B Rev 1.4 with 4G RAM, and starting with the
initial F35 kernel, 5.14.10-300.fc35.aarch64.

I can boot that kernel from a card in the on-board SD slot, but then it
gets stuck trying to read from that card, with looping errors like:

mmc0: error -22 whilst initialising SD card
mmc0: invalid bus width

So I moved the card to a USB adapter. This is a problem for me, because
then I can't set the uboot environment variable to disable stdin from
the serial port (so my GPS HAT input on the serial port stops boot);
that's why I was using the EDK2 EFI firmware, but for these tests, I
stuck with the Fedora-provided uboot firmware and just typed "boot"
every time.

When I remove the /boot/dtb symlink and edit /boot/efi/config.txt to
comment out the "dtoverlay=upstream-pi4" lien and add the following:


I get my PPS and ttyACM0 devices. Yay, desired outcome.

Next, I updated the kernel (to 5.16.11-200.fc35) and uboot-images-armv8
and ran rpi-uboot-update. After reboot, I don't get /dev/pps0, and
there's the error:

pps-gpio: probe of pps@4 failed with error -22

So, from earlier responses, it seems there's some issue with the
different device trees, included with the kernel vs. not? If I use the
kernel-included device tree (I guess by not removing /boot/dtb), how do
I get the overlays so I can use my GPS hat?

Interesting, when I boot 5.16.11-200.fc35 with the /boot/dtb symlink, I
lose HDMI signal a little after the kernel loads (I've removed "rhgb
quiet" from the boot arg). I can see some kernel messages, but then I
lose HDMI. SSHing in, I see in dmesg:

[drm] Initialized vc4 0.0.0 20140616 for gpu on minor 0
Unable to handle kernel read from unreadable memory at virtual address 0000000000000348

and so on with a kernel Oops dump. So it seems the kernel-included
device tree has its own problems on a Pi 4.

Chris Adams <>
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