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

[anish singh]

On Sat, Feb 1, 2014 at 1:03 AM, m silverstri
<michael.j.silverstri at gmail.com> wrote:
> On Sat, Feb 1, 2014 at 12:48 AM, anish singh
> <anish198519851985 at gmail.com> wrote:
>> On Sat, Feb 1, 2014 at 12:32 AM, m silverstri
>> <michael.j.silverstri at gmail.com> wrote:
>> don't top-post
>>
>>> In my driver code,
>>> I want to set a bit in a  HW Register 1. HW will send an interrupt
>> Yes this is how most drivers work.
>>
>>> when setting the register is done.
>>> I don't want my driver code to block until the interrupt is sent from the HW.
>> so i suppose this is what you want to do.
>>
>>
>> write ->register->interrupt happens->disable register ->handle interrupt
>> --->enable register.
>> Look at any driver code from linux kernel code and it mostly does this.
>>>
>
> Thanks.
> But I want my driver code to block until I get the interrupt from HW.

if (driver code == interrupt handler) {
   it_is_not_running_anyway_as_there_is_no_interrupt
} else {
   i don't know what you mean by driver code here?
}
>
>
>
>>>
>>>
>>> On Sat, Feb 1, 2014 at 12:06 AM, anish singh
>>> <anish198519851985 at gmail.com> wrote:
>>>> On Fri, Jan 31, 2014 at 11:55 PM, m silverstri
>>>> <michael.j.silverstri at gmail.com> wrote:
>>>>> Hi,
>>>>>
>>>>> I read this article http://www.linuxjournal.com/article/5833 to learn
>>>>> about spinlock. I try this to use it in my kernel driver.
>>>>>
>>>>> Here is what my driver code needs to do:
>>>>> In f1(), it will get the spin lock, and caller can call f2() will wait
>>>>> for the lock since the spin lock is not being unlock. The spin lock
>>>>> will be unlock in my interrupt handler (triggered by the HW).
>>>> Wrong design!!!
>>>>>
>>>>> void f1() {
>>>>> spin_lock(&mylock);
>>>>> // write hardware
>>>>> REG_ADDR += FLAG_A;
>>>> So here you take spinlock and release in interrupt handler.What
>>>> if there is no interrupt handler and someone calls this fucntion
>>>> he will blocked forever.
>>>>>
>>>>> }
>>>>>
>>>>> void f2() {
>>>>> spin_lock(&mylock);
>>>>> //...
>>>>> }
>>>>>
>>>>> The hardware will send the application an interrupt and my interrupt
>>>>> handler will call spin_unlock(&mylock);
>>>>>
>>>>> My question is if I call
>>>>> f1()
>>>>> f2() // i want this to block until the interrupt return saying settingyou
>>>>> REG_ADDR is done.
>>>>>
>>>>> when I run this, I get an exception in kernel saying a deadlock "
>>>>> INFO: possible recursive locking detected"
>>>>>
>>>>> How  can I re-write my code so that kernel does not think I have a deadlock?
>>>>>
>>>>> I want my driver code to wait until HW sends me an interrupt saying
>>>>> setting REG_ADDR is done.
>>>> Let us know what is your requirement?I am sure there must be a simple
>>>> way to handle than this magic done here.
>>>> Explain what are you trying to do in detail and I am sure lot of
>>>> people will jump
>>>> to help.
>>>>>
>>>>> Thank you.
>>>>>
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