How to make FIQ work with vanilla kernel 3.18?

joshuaclayton — Wed, 31 Dec 2014 19:50:30 GMT

I am having trouble getting a FIQ enabled wtih linux 3.18

We have an application that takes data from a FPGA over the EIM bus at 50kHz.

Porting to 3.18, the old code causes a panic.

I switch ed to use enable_fiq(), and it almost works. It just seems to fall back to the GIC. (I see about 50k interrupts per second in a spurious Irq handler that is set up with request_irq(), but not enabled)

More seriously, I cannot figure out how to put those irq's on cpu 3.

As a result of cpu0 resource contention with network irqs, my userspace application doesn't get all the data...

int evi_init_fiq(struct evifpga_device *dev)

{

int ret;

disable_fiq(dev->irq);

ret = claim_fiq(&fiq_handle);

if (ret) {

printk(KERN_ALERT "EVi - Unable to claim FIQ\n");

return ret;

}

set_fiq_handler(&evi_fiq_handler, SZ_256);

enable_fiq(dev->irq);

if (ret) {

printk(KERN_ALERT "EVi - Unable to enable FIQ on CPU %d\n", FIQ_CPU_TARGET);

release_fiq(&fiq_handle);

return ret;

}

return 0;

}

On 3.0.35 We used a FIQ interrupt on cpu core 3, and then added an isolcpu=3 to the kernel command line to get reliable 50k data.

fiq was enabled by the following:

void fiq_enable(void * data)

{

unsigned long val;

val = readl(GIC_CPU_CTRL);

val |= GIC_CPU_CTRL_BITS_FIQEN;

writel(val, GIC_CPU_CTRL);

}

I noticed that several of the needed address macros were not exported, and attempts to define them but leave the code otherwise untouched resulted in a kernel panic.

GIC_CPU_CTRL is defined as 0x0 (address ZERO!!!111!!) in 3.0.35, so I'm not sure how this ever worked, but it did.

Message was edited by: Joshua Clayton Remove the reference to initiating the FIQ on a specific cpu core. I don't need this anymore

Re: How to make fiq.c code work with kernel 3.18 on a specific cpu core?

fabio_estevam — Fri, 02 Jan 2015 01:03:17 GMT

Maybe you could try asking this one at linux-arm-kernel mailing list.

Re: How to make fiq.c code work with kernel 3.18 on a specific cpu core?

joshuaclayton — Mon, 12 Jan 2015 20:11:16 GMT

After some trepidation, I went ahead and posted to the arm kernel mailing list.

I never did get a response on the arm kernel mailing list. The best I have found so far are patches posted by Daniel Thompson, which purport to enable some NMI like interrupts to use the FIQ mechanism.

I'm now taking a second look after doing other things for a while. So far I have not had success.

topic Re: How to make fiq.c code work with kernel 3.18 on a specific cpu core? in i.MX Processors

How to make FIQ work with vanilla kernel 3.18?

Re: How to make fiq.c code work with kernel 3.18 on a specific cpu core?

Re: How to make fiq.c code work with kernel 3.18 on a specific cpu core?