How to use enable the FIQ with the ARM timer on rpi zero in my driver?

s.achterop at s.achterop at
Mon Apr 13 05:11:39 EDT 2020

   Hello List,
I am on a raspberry pi zero, chipset BCM2835, and try to use the ARM timer to get FIQ interrupts.
I compiled the kernel from source to be able to create my out-of-tree module. Uname -a gives:
     Linux raspberrypi 4.19.108+ #1 PREEMPT Tue Mar 31 10:00:18 CEST 2020 armv6l GNU/Linux
       (i only set it to be a low-latency-kernel)

I try to create an fiq interrupt in a number of ways, but nothing works.
The driver I created can be found at

The ARM timer is configured by directly writing to the registers.
It is running fine and sets it's interrupt bit at some point.
So I assume that linux does not use the ARM timer in a base configuration.

When using:

  ret = claim_fiq(&bat_fh);
  set_fiq_handler(&batradio_handler, &batradio_handler_end - &batradio_handler);

There are no fiq interrupts, i tried several values of x.
My main question is, which irq number should I use.

Note that I use
     pdev = platform_device_register_simple("batradio__", 0, NULL, 0);
to register this platform device.

I did find a complete example in
But there they used a device tree and got the fiq-irq number via the probe function argument.
Maybe that is a way to get it working, but I don't know with compatible value to use.

I also tried, instead of enable_fiq, to directly connect the ARM timer to FIQ by
writing 0xC0, 0x80 + 0x40, to the FIQ Control register 0x20C.
But then Linux freezes immediately, so that's probably the wrong way.

What could I do to get FIQ interrupts working? Or where can I find which irq number to use in enable_fiq?

    Hopefully someone can point me in a direction.
       Thanks in advance,

PS. I forced dwc_otg to not use fiq by adding the following to /boot/cmdline.txt
         dwc_otg.fiq_fsm_enable=0 dwc_otg.fiq_enable=0 dwc_otg.nak_holdoff=0

     I also make it boot up with console, so no X stuff, and access via ssh.

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