Friday, April 22, 2022

[fedora-arm] Re: Raspberry Pi PoE HAT

Fedora Arm Community -

Ben Herrick and I exchanged several messages about Fedora 36 and
Fedora 35. I was successful in getting the POE Hat fan to work with
Fedora 36 (beta) using a couple of the steps as outlined in the Fedora
wiki for RPI Hats but was not as successful with Fedora 35. I suspect
it should work as long as current firmware files are used (e.g.
start4.elf) but in my very limited testing with FC35, I could not get
the board to boot and I was too lazy to pull the headless board from
the rack to plug a monitor and keyboard to see where the boot was

My original process involving a custom upstream device tree to
integrate with the POE Hat fan device driver still works fine for FC35
and FC34.

For Fedora 36 (beta) I found that if I followed the steps in the wiki
to load the firmware device tree (rm /boot/dtb and set FirmwareDT=true
in /etc/u-boot.conf) then the POE Hat fan would just work as long as I
also made sure the upstream_kernel=1 option in config.txt was
commented out.

I did not need to add the rpi-poe or i2c dtoverlay lines to
config.txt. This process worked on 3 RPi4 boards that were updated
from FC35 using dnf system upgrade and which use u-boot. A fourth RPi4
using UEFI was also updated to FC36 beta with upstream_kernel=1
commented out and the POE Hat fan also worked without any additional
configuration. All 4 boards are 8 GB and all 4 POE Hats are the
original model.

The device tree can be inspected at /proc/device-tree and will show a
directory called pwm-fan which is the hook needed for the upstream fan
device driver. lsmod can be used to display the presence of the
pwm_raspberrypi_poe device driver that makes all of this happen as
long as the linux kernel is 5.13 or newer (if i recall correctly).

Glad to answer any questions.



On Mon, Apr 18, 2022 at 7:15 AM Ben Herrick <> wrote:
> Fedora ARM mailing list,
> I've been trying to get the fan on my Raspberry Pi PoE HAT working with Fedora 35 and 36 Beta. I'm using the aarch64 raw image.
> I came across the instructions on the wiki page here:
> Unfortunately, the line in config.txt from the wiki didn't work for me.
> The lines that did work on Fedora 36 Beta for aarch64 are below:
> dtoverlay=i2c
> dtoverlay=pwm-raspberrypi-poe
> I'm also able to set the fan parameters with the below:
> dtparam=poe_fan_temp0=70000,poe_fan_temp0_hyst=10000
> dtparam=poe_fan_temp1=60000,poe_fan_temp1_hyst=10000
> dtparam=poe_fan_temp2=50000,poe_fan_temp2_hyst=10000
> dtparam=poe_fan_temp3=40000,poe_fan_temp3_hyst=10000
> Note that these same lines didn't work for me on Fedora 35 aarch64.
> I'm hoping others can replicate my experience and the wiki can be updated to help others.
> Please let me know if you have any questions or concerns.
> -Ben Herrick
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