[Linux-stm32] STM32MP1 level triggered interrupts

[Marek Vasut]

On 1/23/20 10:22 AM, Marc Zyngier wrote:
> On 2020-01-23 08:27, Alexandre Torgue wrote:
>> On 1/22/20 8:29 PM, Marek Vasut wrote:
>>> On 1/22/20 6:19 PM, Alexandre Torgue wrote:
>>>
>>> Hi,
>>>
>>> [...]
>>>
>>>>>> Concerning, your question:
>>>>>>
>>>>>> Setting your gpioC interruption as "falling edge" should be
>>>>>> enough. On
>>>>>> gpioCx falling edge, a high-level signal is generated by exti and
>>>>>> sent
>>>>>> to GIC (which triggers GIC interrupt). This signal remains high until
>>>>>> stm32_irq_ack is called.
>>>>>>
>>>>>> So you only need: (ex for gpioc 1).
>>>>>>
>>>>>> interrupt-parent = <&gpioc>;
>>>>>> interrupts = <1 IRQ_TYPE_EDGE_FALLING>;
>>>>>
>>>>> How does this deal with the case where the device holds the interrupt
>>>>> line low (since it's level-sensitive, active low) after the driver
>>>>> interrupt handler finishes ? Does such condition generate another
>>>>> interrupt and call the driver interrupt handler again ? I would expect
>>>>> the answer is no, because the interrupt is edge-triggered and there is
>>>>> no edge.
>>>>
>>>> Your assumption is good. If your device continue to hold the line to
>>>> low
>>>> at the end of your interrupt handler, no more interrupt will be
>>>> generated.
>>>
>>> But does that basically mean that such a device cannot be used with
>>> STM32MP1 or am I fundamentally mistaken and don't understand how a
>>> level-triggered interrupt works ? :)
>>
>> You need to release the line in your device interrupt handler. If not,
>> yes, you will miss interrupts :$
> 
> So to sum it up, this SoC doesn't support external level interrupts
> on its own, full stop. You'd need some additional external sampling
> HW to retrigger an edge on EOI.

Thank you for confirming my suspicion.