[fedora-arm] Re: device tree on Pi4B

On Wed, Aug 3, 2022 at 4:17 PM Steven A. Falco <stevenfalco@gmail.com> wrote:
>
> I have a Pi4B that is working pretty well with the aarch64 version of Fedora Rawhide, but I have one issue that I haven't been able to find a solution to.
>
> I have an Adafruit RTC connected via I2C (https://www.adafruit.com/product/3386). If I use the kernel device tree, this device is not found.
>
> I then tried switching to the firmware device tree via the instructions in https://fedoraproject.org/wiki/Architectures/ARM/Raspberry_Pi/HATs. That works pretty well - I can now add an overlay for the RTC in /boot/efi/config.txt and the RTC is found during boot. dtoverlay=i2c-rtc,pcf8523,addr=0x68
>
> However, once I've switched to the firmware device tree, I no longer have /dev/vchiq, which means that I can no longer use vcgencmd. Instead, vcgencmd gives me "VCHI initialization failed".

It should be the same as required in Raspbian. Have you checked the
details in /boot/efi/overlays/README? Out of interest what do you use
/dev/vchiq / vcgencmd for?

> Is there any way to get both the RTC and vcgencmd to work? Which device tree would I choose? Do I have to build a custom kernel or is there some other way to enable the RTC with the kernel device tree?

You don't need a custom kernel but you'd need to build your own DT as
obviously anything that is not default on the RPi devices themselves
is optional hence the requirement of overlays.
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