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SubjectRe: [PATCH 3/3] iio: st_sensors: Use level interrupts
On 24/05/16 13:35, Crestez Dan Leonard wrote:
> On 05/24/2016 02:40 PM, Linus Walleij wrote:
>> On Fri, May 13, 2016 at 8:43 PM, Crestez Dan Leonard
>> <> wrote:
>>> As far as I can tell DRDY for ST sensors behaves as a level rather than
>>> edge interrupt. Registering for IRQF_TRIGGER_RISING instead of
>>> IRQF_TRIGGER_HIGH mostly works except when the sampling frequency is
>>> high enough that new samples come before the new ones are read
>>> completely. In that case the interrupt line remains high, no more rising
>>> edges occur and the iio buffer stalls.
>>> Configuring the interrupt as IRQF_TRIGGER_HIGH makes it work as
>>> expected. This patch makes it so that st_sensors_trigger interrupt
>>> request code doesn't mangle the request flags into IRQF_TRIGGER_RISING.
>>> Cc: Linus Walleij <>
>>> Cc: Giuseppe Barba <>
>>> Cc: Denis Ciocca <>
>>> Signed-off-by: Crestez Dan Leonard <>
>> The analysis is probably correct: the sensors will hold the line low
>> until the values have been read and no data is ready in the pipe.
>> This is delicate when the sensors are used with GPIO controllers
>> as interrupt line handlers, because some of them (like mine
>> on Ux500) do not support level interrupts :(
> This might be completely crazy, but wouldn't it be possible to support
> gpio level interrupts purely in software? Just read the GPIO state again
> after the interrupt is unmasked and retrigger.
> This seems preferable to implementing per-driver workarounds. Perhaps it
> would even fit in some gpio-irqchip glue.
That's precisely the question I raised way back when writing the lis3l02dq
driver. Apparently someone once had a go but it never went anywhere...

Feel free to try! It would be great if possible.


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