[meta-freescale] imx6Q: sdma produces a large number of interrupts

George Kang georgekang03 at gmail.com
Sat Jul 16 06:28:39 PDT 2016

Hi all,

Sometimes, sdma produces a large number of interrupts without a stop, and
Linux kernel might freeze. This situation

happens in kernel with PREEMPT_RT in some specific configuration for
islocpu. Currently, the kernel in my test is

Linux 4.1.15-rt17 and the kernel command line is

console=ttymxc0,115200 root=/dev/mmcblk0p2 rootwait rw nohz_full=3
isolcpus=1,2 nohz=on

After booting, the kernel will freeze and the last messages are:

   imx-weim 21b8000.weim: Driver registered.

    imx-sdma 20ec000.sdma: failed to get firmware from device tree

    imx-sdma 20ec000.sdma: initialized

    2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 24, base_baud =

    5000000) is a IMX

    console [ttymxc0] enabled

    random: nonblocking pool is initialized

The last line give me a hint and I find add_interrupt_randomness() from
irq_thread is called continuously

Then I insert a printk in irq_thread(void *data) to identify the interrupt
source for this issue.

It shows 281, which is the interrupt number of sdma, and never stops.

In my root fs, the firmware for sdma does not exist and the number of sdma
interrupt is only two in ordinary booting.

Is there any suggestion to investigate this issue?

Thanks a lot.

Best Regards,

George Kang
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