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From: Ville Syrjälä on 26 Feb 2010 14:10
On Fri, Feb 26, 2010 at 06:33:57PM +0100, Rafał Miłecki wrote:
> W dniu 26 lutego 2010 17:14 użytkownik Andrew Morton
> <akpm(a)linux-foundation.org> napisał:
> > On Fri, 26 Feb 2010 11:38:59 +0100 Rafa Miecki <zajec5(a)gmail.com> wrote:
> >
> >> +#define wait_interruptible_timeout(wq, timeout)
> >>     \
> >> +({                                   \
> >> +    long ret = timeout;                      \
> >> +                                    \
> >> +    DEFINE_WAIT(wait);                      \
> >> +    prepare_to_wait(&wq, &wait, TASK_INTERRUPTIBLE);       \
> >> +    if (!signal_pending(current))                  \
> >> +        ret = schedule_timeout(ret);            \
> >> +    finish_wait(&wq, &wait);                   \
> >> +                                    \
> >> +    ret;                             \
> >> +})
> >
> > It's often a mistake to use signals in-kernel.  Signals are more a
> > userspace thing and it's better to use the lower-level kernel-specific
> > messaging tools in-kernel.  Bear in mind that userspace can
> > independently and asynchronously send, accept and block signals.
>
> Can you point me to something kernel-level please?
>
>
> > Can KMS use wait_event_interruptible_timeout()?
>
> No. Please check definition of this:
>
> #define wait_event_interruptible_timeout(wq, condition, timeout) \
> ({ \
> long __ret = timeout; \
> if (!(condition)) \
> __wait_event_interruptible_timeout(wq, condition, __ret); \
> __ret; \
> })
>
> It uses condition there, but that's not a big issue. We just need to
> pass 0 (false) there and it will work so far.

Disabling the condition check doesn't make sense.

You could use a completion.

init_completion(vbl_irq);
enable_vbl_irq();
wait_for_completion(vbl_irq);
disable_vbl_irq();
and call complete(vbl_irq) in the interrupt handler.

The same would of course work with just some flag or counter
and a wait queue. Isn't there already a vbl counter that you could
compare in the condition?

--
Ville Syrjälä
syrjala(a)sci.fi
http://www.sci.fi/~syrjala/
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