Delaying an interrupt handler

Delaying an interrupt handler

[Milton Krutt]

Hi.
It is known that no semaphore synchronization should be
used inside an interrupt handler.

Anyway, I am looking at a freeBSD device driver (written by
a profesionist) and there are semaphores inside an interrupt
handler's subroutine.

Since I should port to linux that driver, I ask you how can I
reach such synchronization under linux; I tried to use semaphores
inside my handler but I got complains, and I don't want to break
the law, so no semaphores for me.

The scenario is the following:

firmware downloader {

while(fw_blocks--){

/* the call below will cause an interrupt */
load_block();

/* sleep unitl the int handler ackn's the previous
operation, and prevent ANY int. handler operations
until the process goes actually to sleep through the
following call */

sleep();      }
	  }


int handler {

if(the process is NOT asleep)
	wait();

wake up the process.
			}


NOTE: I am on a 2.6.10 in order to be closely tutored by LDD3.

Delaying an interrupt handler

[Daniel Baluta]

On Mon, Mar 23, 2015 at 2:18 PM, Milton Krutt <milton@krutt.org> wrote:
> Hi.
> It is known that no semaphore synchronization should be
> used inside an interrupt handler.
>
> Anyway, I am looking at a freeBSD device driver (written by
> a profesionist) and there are semaphores inside an interrupt
> handler's subroutine.
>
> Since I should port to linux that driver, I ask you how can I
> reach such synchronization under linux; I tried to use semaphores
> inside my handler but I got complains, and I don't want to break
> the law, so no semaphores for me.

Perhaps spinlocks could be the solution :).

2.6.10 please no - :), Linux kernel is now at 4.0.

Daniel.

Delaying an interrupt handler

[Milton Krutt]

> On Mon, Mar 23, 2015 at 2:18 PM, Milton Krutt <milton@krutt.org> wrote:
> > Hi.
> > It is known that no semaphore synchronization should be
> > used inside an interrupt handler.
> >
> > Anyway, I am looking at a freeBSD device driver (written by
> > a profesionist) and there are semaphores inside an interrupt
> > handler's subroutine.
> >
> > Since I should port to linux that driver, I ask you how can I
> > reach such synchronization under linux; I tried to use semaphores
> > inside my handler but I got complains, and I don't want to break
> > the law, so no semaphores for me.
> 
> Perhaps spinlocks could be the solution :).
> 
> 2.6.10 please no - :), Linux kernel is now at 4.0.
> 
> Daniel.

Yes and no. The routine the int. handler's delay depends on has to
make some non atomic work. So if I lock a spinlock and then I do some
"lengthy" (i.e. non atomic) job, then I get a warning message like
"spinlock held while being preempted" (or similar). In symbols, you suggest
something like

process P{

spin_lock(lock);
non_atomic_function();
spin_unlock(lock);

}

int. handler {

spin_lock(lock);
do_things(); /* preferably atomically */
spin_unlock(lock);

}

My first attempt is still to avoid both semaphores and the above remedy,
in order to delay the int. handler up to a desired point.

Thanks!