Problem Summary
EPOLLERR is always set, as part of epoll_wait() return status, even under no error condition.
Platform Summary
- i.MX6SDL Board
- Kernel Version :: 4.1.15
- rootfs :: Ubuntu Xenial repo
Description
From user space app, I use epoll mechanism to monitor & capture GPIO events.
Functionality looks ok as expected. but I observe EPOLLERR ( epoll event flag ) is
always set, but epoll_wait() returns +ve return value ( indicates no error ).
I tried to investigate the source of event flag EPOLLERR.
With help of ftrace (ftrace-function-flowgraph.zip), I managed
to get the below simplified sequence flow graph (epoll-gpio-EPOLLERR-trace-sfg.png).
I unable to trace out How IMX GPIO ISR status value is get transformed
to ePoll event flags in below simplified ISR sequence flow.
gic_handle_irq() {irq-gic.c} --> \
mx3_gpio_irq_handler() {gpio-mxc.c} [ reading & broadcasting GPIO_ISR status value ] --> \
gpio_sysfs_irq() {gpiolib-sysfs.c} --> \
ep_poll_callback() {eventpoll.c}
Note :: I tried with different set of epoll event mask to epoll_ctl() &
with increased timeout value to epoll_wait(). But no change in behaviour.
Like to know in community does any one come across similar kind of issue.
