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SubjectRe: [Linuxarm] [PATCH for next v1 0/2] gpio: few clean up patches to replace spin_lock_irqsave with spin_lock

On 2021/2/9 17:42, Andy Shevchenko wrote:
> On Tue, Feb 9, 2021 at 11:24 AM luojiaxing <> wrote:
>> On 2021/2/8 21:28, Andy Shevchenko wrote:
>>> On Mon, Feb 8, 2021 at 11:11 AM luojiaxing <> wrote:
>>>> Sorry, my operation error causes a patch missing from this patch set. I
>>>> re-send the patch set. Please check the new one.
>>> What is the new one?! You have to give proper versioning and change
>>> log for your series.
>> sure, I will send a new one later, but let me answer your question first.
>>>> On 2021/2/8 16:56, Luo Jiaxing wrote:
>>>>> There is no need to use API with _irqsave in hard IRQ handler, So replace
>>>>> those with spin_lock.
>>> How do you know that another CPU in the system can't serve the
> The keyword here is: *another*.

ooh, sorry, now I got your point.

As to me, I don't think another CPU can serve the IRQ when one CPU
runing hard IRQ handler,

except it's a per CPU interrupts.

The following is a simple call logic when IRQ come.

elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq ->

Assume that two CPUs receive the same IRQ and enter the preceding
process. Both of them will go to desc->handle_irq().

In handle_irq(), raw_spin_lock(&desc->lock) always be called first.
Therefore, even if two CPUs are running handle_irq(),

only one can get the spin lock. Assume that CPU A obtains the spin lock.
Then CPU A will sets the status of irq_data to

IRQD_IRQ_INPROGRESS in handle_irq_event() and releases the spin lock.
Even though CPU B gets the spin lock later and

continue to run handle_irq(), but the check of irq_may_run(desc) causes
it to exit.

so, I think we don't own the situation that two CPU server the hard IRQ
handler at the same time.

>>> following interrupt from the hardware at the same time?
>> Yes, I have some question before.
>> There are some similar discussion here, please take a look, Song baohua
>> explained it more professionally.
>> Here are some excerpts from the discussion:
>> I think the code disabling irq in hardIRQ is simply wrong.
> Why?

I mention the following call before.

elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq ->

__handle_domain_irq() will call irq_enter(), it ensures that the IRQ
processing of the current CPU can not be preempted.

So I think this is the reason why Song baohua said it's not need to
disable IRQ in hardIRQ handler.

>> Since this commit
>> genirq: Run irq handlers with interrupts disabled
>> interrupt handlers are definitely running in a irq-disabled context
>> unless irq handlers enable them explicitly in the handler to permit
>> other interrupts.
> This doesn't explain any changes in the behaviour on SMP.
> IRQ line can be disabled on a few stages:
> a) on the source (IP that generates an event)
> b) on IRQ router / controller
> c) on CPU side

yes, you are right.

> The commit above is discussing (rightfully!) the problem when all
> interrupts are being served by a *single* core. Nobody prevents them
> from being served by *different* cores simultaneously. Also, see [1].
> [1]:

I check [1], quite useful description about locking, thanks. But you can

see Table of locking Requirements

Between IRQ handler A and IRQ handle A, it's no need for a SLIS.




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