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

From: Alexandre Torgue
Date: Thu Feb 20 2020 - 08:09:55 EST

Hi Marek

On 2/19/20 6:24 PM, Marek Vasut wrote:
On 2/19/20 10:20 AM, 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
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
as trigger-level-low and gpioD2 set as trigger-edge-falling ? It seems
8eb2dfee9fb1 ("pinctrl: stm32: add lock mechanism for irqmux
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.

Considering the EXTI line limitations, I'd like to know what kind of IRQ
input configuration is allowed/valid and what kind of configuration is
not valid.

As a mux is used to select which GPIO[A..Z]_X has to be mapped on exti_X line, only one GPIO can be used on the EXTI line.

For example, on EXTI2 you could map either gpioa2 or gpiob2 or ....gpioz2 but not gpioa2 and gpiob2 in the same time.

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

Â|--> stm32_exti_set_type type -> change exti line 2 trigger registers

stm32_gpio_domain_activate --> failed as exti line2 is already used

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.

So the hardware does support using both gpioA2 and gpioB2 as an
interrupt source, for different drivers, if they are of the same
interrupt type. Except the current implementation does not permit that.

No hardware doesn't allow it for reason explain above.

If the interrupt types are different, that is not supported by the hardware.

Correct ?