linux-kernel - Re: iio: dht11 broken

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Date:	Mon, 01 Dec 2014 11:59:50 +0100
From:	Richard Weinberger <richard@....at>
To:	Harald Geyer <harald@...ib.org>
CC:	linus.walleij@...aro.org, linux-gpio@...r.kernel.org,
	javier.martinez@...labora.co.uk, acourbot@...dia.com,
	swarren@...dia.com, jic23@...nel.org, knaack.h@....de,
	lars@...afoo.de, pmeerw@...erw.net, linux-iio@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: iio: dht11 broken

Hi!

Am 01.12.2014 um 11:49 schrieb Harald Geyer:
> Hi Richard!
> 
> Richard Weinberger writes:
>> Staring with 3.12 gpiolib refuses to set an GPIO used as IRQ into output mode.
>> see commit d468bf9e (gpio: add API to be strict about GPIO IRQ usage)
>> The dht driver does this and is therefore not functional.
>> As the dht11 driver got merged in 3.13 there is a high chance that it
>> never worked.
> 
> Well, I'm developing on mxs and there it works on 3.13 and 3.14 at least.
> (I have it in production using 3.14.18 ATM.)
>  
>> Harald, are you aware of this issue?
> 
> I got one report about this issue, but couldn't reproduce it yet and
> the reporter didn't agree to quoting his messages to kernel mailing lists,
> so this has been rather low priority on my todo list. Next plan is to
> see if I can reproduce the issue on sunxi (A10).

Not all gpio drivers use the new IRQ lock stuff.

> However anybody able to reproduce this and willing to test patches, would
> of course push this up on my todo list.
> 
> Any input from gpiolib people about what the proper fix would be in
> their opinion, of course is appreciated. I don't think the dht11 driver
> is doing anything unreasonable per se, so maybe they can clarify how
> the API is intended to be used?

Your driver sets up a GPIO as IRQ and then you switch the mode to output
to enable the DHT sensor.
This is not an API issue, it is an design issue.
I'm not a hardware expert but AFAIK setting an IRQ pin into output mode can
lead to undefined behavior.

Thanks,
//richard
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