linux-kernel - Re: iio: dht11 broken

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Message-ID: <CACRpkdbSUJMF_1_8aZ+ECHAT+ztsa4jXuSFo_+V9gr1MzsNCcg@mail.gmail.com>
Date:	Mon, 1 Dec 2014 15:08:45 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Richard Weinberger <richard@....at>
Cc:	Harald Geyer <harald@...ib.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Alexandre Courbot <acourbot@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: iio: dht11 broken

On Mon, Dec 1, 2014 at 11:59 AM, Richard Weinberger <richard@....at> wrote:
> Am 01.12.2014 um 11:49 schrieb Harald Geyer:

>> 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.

Well that check is there exactly to prevent madness like this.

IRQs on pins set to output *does* *not* *make* *sense*.

Remove the IRQ before setting the pin to output and vice
versa and everyone will be happier.

Yours,
Linus Walleij
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