On 9/24/2020 11:06 PM, Felipe Balbi wrote:
>
> Hi,
>
> Alan Stern <st...@rowland.harvard.edu> writes:
>>>> Hence, the reason if there was already a pending IRQ triggered, the
>>>> dwc3_gadget_disable_irq() won't ensure the IRQ is handled. We can do
>>>> something like:
>>>> if (!is_on)
>>>> dwc3_gadget_disable_irq()
>>>> synchronize_irq()
>>>> spin_lock_irqsave()
>>>> if(!is_on) {
>>>> ...
>>>>
>>>> But the logic to only apply this on the pullup removal case is a little
>>>> messy. Also, from my understanding, the spin_lock_irqsave() will only
>>>> disable the local CPU IRQs, but not the interrupt line on the GIC, which
>>>> means other CPUs can handle it, unless we explicitly set the IRQ
>>>> affinity to CPUX.
>>>
>>> Yeah, the way I understand this can't really happen. But I'm open to
>>> being educated. Maybe Alan can explain if this is really possibility?
>>
Hi Felipe/Alan,
Thanks for the detailed explanations and inputs. Useful information to
have!
>> It depends on the details of the hardware, but yes, it is possible in
>> general for an interrupt handler to run after you have turned off the
>> device's interrupt-request line. For example:
>>
>> CPU A CPU B
>> --------------------------- ----------------------
>> Gets an IRQ from the device
>> Calls handler routine spin_lock_irq
>> spin_lock_irq Turns off the IRQ line
>> ...spins... spin_unlock_irq
>> Rest of handler runs
>> spin_unlock_irq
>>
>> That's why we have synchronize_irq(). The usual pattern is something
>> like this:
>>
>> spin_lock_irq(&priv->lock);
>> priv->disconnected = true;
>> my_disable_irq(priv);
>> spin_unlock_irq(&priv->lock);
>> synchronize_irq(priv->irq);
>>
>> And of course this has to be done in a context that can sleep.
>>
>> Does this answer your question?
>
> It does, thank you Alan. It seems like we don't need a call to
> disable_irq(), only synchronize_irq() is enough, however it should be
> called with spinlocks released, not held.
>
I mean...I'm not against using the synchronize_irq() +
dwc3_gadget_disable_irq() route, since that will address the concern as
well. It was just with the disable/enable IRQ route, I didn't need to
explicitly check the is_on flag again, since I didn't need to worry
about overwriting the DEVTEN reg (for the pullup enable case). Will
include this on the next version.
Thanks
Wesley Cheng
> Thanks
>
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