linux-kernel - Re: [PATCH v3 6/6] iio: adc: stm32: add support for EXTI trigger

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Date:   Fri, 3 Mar 2017 16:46:39 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Fabrice Gasnier <fabrice.gasnier@...com>, jic23@...nel.org,
        linux@...linux.org.uk, robh+dt@...nel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     linux-iio@...r.kernel.org, mark.rutland@....com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        knaack.h@....de, pmeerw@...erw.net, benjamin.gaignard@...aro.org,
        benjamin.gaignard@...com, linus.walleij@...aro.org
Subject: Re: [PATCH v3 6/6] iio: adc: stm32: add support for EXTI trigger

On 03/03/2017 02:00 PM, Fabrice Gasnier wrote:
> On 03/03/2017 12:45 PM, Lars-Peter Clausen wrote:
>> On 02/28/2017 05:51 PM, Fabrice Gasnier wrote:
>>> EXTi (external interrupt) signal can be routed internally as trigger
>>> source for ADC conversions: STM32F4 ADC can use EXTI11.
>>>
>>> Retrieve interrupt trigger from DT, so it can be muxed into ADC IP,
>>> via extsel.
>>
>> Hi,
>>
>> Sorry, I have some trouble understanding the specifics of this. Is EXTI a
>> hardware input signal into the ADC that automatically triggers a conversion
>> when asserted? If yes how is it configured which external signal is used
>> here. Your bindings suggest that any GPIO can be used, but the driver only
>> differentiates between EXTI on or EXTI off.
> Hi Lars,
> 
> Yes, STM32 EXTI is external interrupt/event line. In case of STM32 ADC,
> EXTI11 signal can be used to start a conversion. In this case, it must
> be selected inside ADC IP using extsel bitfield. This EXTI11 line can
> mapped from any GPIO bank A,B... line 11 (e.g. PA11 or PB11...) by using
> interrupt binding.
> This is why I expose this in DT.

How is the mapping? That's the part I don't understand. How does requesting
the IRQ for the GPIO as a generic software IRQ establish the hardware
connection between the GPIO block and the ADC?