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

[m silverstri]

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


On Sat, Feb 1, 2014 at 1:06 AM, anish singh <anish198519851985 at gmail.com> wrote:
> 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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