linux-kernel - Re: [PATCH v2 0/2] Add GPIO level-sensitive interrupt support

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Message-ID: <d271f09b-6391-779a-b133-66bcdfbb0ec6@st.com>
Date:   Wed, 19 Feb 2020 10:20:26 +0100
From:   Alexandre Torgue <alexandre.torgue@...com>
To:     Marek Vasut <marex@...x.de>, Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] Add GPIO level-sensitive interrupt support



On 2/18/20 7:13 PM, Marek Vasut wrote:
> On 2/18/20 7:10 PM, Alexandre Torgue wrote:
>> Hi Marek
> 
> Hi,
> 
>> On 2/18/20 5:25 PM, Marek Vasut wrote:
>>> On 2/18/20 2:12 PM, Alexandre Torgue wrote:
>>>> This series adds the possibility to handle gpio interrupts on level.
>>>>
>>>> GPIO hardware block is directly linked to EXTI block but EXTI handles
>>>> external interrupts only on edge. To be able to handle GPIO interrupt on
>>>> level a "hack" is done in gpio irq chip: parent interrupt (exti irq
>>>> chip)
>>>> is retriggered following interrupt type and gpio line value.
>>>>
>>>> In exti irq chip, retrigger ops function is added.
>>>
>>> btw. this might be unrelated, but is it possible to have e.g. gpioC2 set
>>> as trigger-level-low and gpioD2 set as trigger-edge-falling ? It seems
>>> 8eb2dfee9fb1 ("pinctrl: stm32: add lock mechanism for irqmux selection")
>>> prevents that.
>>>
>>
>> No it's not possible. Each gpio line doesn't have a dedicated Exti line
>> Each Exti line is muxing between gpio banks.
> 
> OK, that confirms my assumption.
> 
>> Mapping is done as following:
>>
>> EXTI0 = A0 or B0 or C0 .... or Z0 : selected by Mux
>> EXTI1 = A1 or B1 or C1 ....or Z1 : selected by Mux
>> EXTI2 = A2 or B2 or C2 ....or Z2 : selected by Mux
>> ...
> 
> Is it at least possible to have IRQs of the same type on the same exti
> line? E.g. gpioA2 of trigger-edge-falling and gpioB2 trigger-edge-falling ?
> 

Sorry I don't catch your point. If you already succeed to get gpioA2, 
then you will failed to get gpioB2 but looking at function call stack we 
could get an other issue.

Lets take example where you succeed to get gpioa2 as interrupt (using 
interrupt bindings) and now you try to do the same for gpiob2, you will 
have (roughly):

stm32_gpio_irq_request_resources (for gpiob2) --> succeed

stm32_gpio_set_type
  |
  |--> stm32_exti_set_type type -> change exti line 2 trigger registers
                                   with gpiob2 binding.

stm32_gpio_domain_activate --> failed as exti line2 is already used
			       by gpioa2.

So as stm32_gpio_set_type is called before checking than exti line is 
available, type could be changed and behavior of gpioa2 interrupt broken.

Solution would be to move the exti line mux check from 
stm32_gpio_domain_activate to  stm32_gpio_irq_request_resources callback.

Regards
Alex