Re: Fw: [3.18.3] poll() on gpio pins broken

[Alexandre Courbot <gnurou@xxxxxxxxx>]

On Sat, Jan 31, 2015 at 9:33 AM, folkert <folkert@xxxxxxxxxxxxxx> wrote:
> Michael,
>
>> > For timekeeping I wrote a program which waits for interrupts on
>> > gpio-pins and then tells the local ntp daemon the clock offset.
>> > I'm aware of the pps support in recent kernel but that does not work
>> > (yet) on all platforms (eg cubieboard 1).
>> >
>> > This has worked for quite some time but no longer.
>> >
>> > Until at least kernel 3.12 I could do:
>> >
>> > // export gpio pin
>> > // set direction to in
>> > // set direction to rising
>> > int fd = open("/sys.../value", O_RDONLY);
>> > fdset[0].fd = fd;
>> > fdset[0].events = POLLPRI;
>> > fdset[0].revents = 0;
>> > poll(fdset, 1, -1);
>> > // at this point pin went high
>>
>> Try using lseek before reading the data after the poll.
>>
>> EX.
>>       if (fdset[0].revents & POLLPRI) {
>>               lseek(fdset[0].fd, 0, SEEK_SET);
>>               len = read(fdset[0].fd, buf, MAX_BUF);
>>               .
>>               .
>>       }
>>
>> See if this helps.
>
> Yes, that fixed it!

Still, shouldn't we consider this as a regression, especially if not
using lseek worked for kernel 3.12 and before?

Linus, what do you think?
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