Question about using spinlock to synchronize between kernel driver and an interrupt handler

[Arun KS]

Hi Silverstri,


On Sun, Feb 2, 2014 at 1:19 PM, m silverstri <michael.j.silverstri at gmail.com
> wrote:

> On Sat, Feb 1, 2014 at 5:34 AM, Josh Cartwright <joshc at eso.teric.us>
> wrote:
> > On Sat, Feb 01, 2014 at 01:32:49AM -0800, anish singh wrote:
> >> On Sat, Feb 1, 2014 at 1:15 AM, m silverstri
> >> <michael.j.silverstri at gmail.com> wrote:
> >> > By driver code , I mean the code which set the register values and
> >> > wait till the values is set (via an interrupt handler) before
> >> > continues doing something else
> >> ok so you are looking for below code:
> >>
> >>
> >> some_func()
> >> {
> >> set_register_value
> >> x_variable=0
> >> wait_for_event*(x_variable);
> >> }
> >>
> >> interrupt_handler(){
> >> x_variable=1
> >> wake_up();
> >> }
> >>
> >> request_irq(interrupt_handler);
> >
> > Please investigate the usage of completions in your driver.  See
> > include/linux/completion.h.  It sounds like it fits your usecase nicely.
> >
> >   Josh
>
> I have loooked at linux completion for my usecase
> So I think I can do
>
> DECLARE_COMPLETION(my_completion);
>
> some_func()
> {
> set_register_value
> wait_for_completion(my_completion);
> }
>
> interrupt_handler(){
> complete(my_completion);
> }
>
> request_irq(interrupt_handler);
>
>
> My question now is what if 1 kernel thread execute some_funct(), but
> before interrupt_handler() get invoked (from HW), another kernel
> thread executes some_func(). In essence, set_register_value is execute
> twice before interrupt_handler() return once.
>
Use a mutex_lock().
So your code will be as follows:

DECLARE_COMPLETION(my_completion);
struct mutex dev_lock;

some_func()
{
mutex_lock(&dev_lock);
set_register_value
wait_for_completion(my_completion);
mutex_unloc(&dev_lock);
}

interrupt_handler(){
complete(my_completion);
}

mutex_init(&dev_lock);
request_irq(interrupt_handler);

Thanks,
Arun


>
> how can I prevent another kernel thread from executing
> "set_register_value()" when 1 is wait_for_completion?
>
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