Re: [RFCv4 06/11] misc: Introduce Nokia CMT driver

From: Linus Walleij <linus.walleij@linaro.org>
To: "Linus Walleij" <linus.walleij@linaro.org>,
	"Shubhrajyoti Datta" <omaplinuxkernel@gmail.com>,
	"Carlos Chinea" <cch.devel@gmail.com>,
	"Tony Lindgren" <tony@atomide.com>,
	"Grant Likely" <grant.likely@linaro.org>,
	"Rob Herring" <rob.herring@calxeda.com>,
	"Pawel Moll" <pawel.moll@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Stephen Warren" <swarren@wwwdotorg.org>,
	"Ian Campbell" <ijc+devicetree@hellion.org.uk>,
	"Rob Landley" <rob@landley.net>,
	"Benoît Cousson" <bcousson@baylibre.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux-OMAP <linux-omap@vger.kernel.org>,
	"Pali Rohár" <pali.rohar@gmail.com>,
	"Ивайло Димитров" <freemangordon@abv.bg>,
	"Joni Lapilainen" <joni.lapilainen@gmail.com>,
	"Aaro Koskinen" <aaro.koskinen@iki.fi>
Subject: Re: [RFCv4 06/11] misc: Introduce Nokia CMT driver
Date: Mon, 16 Dec 2013 14:31:53 +0100	[thread overview]
Message-ID: <CACRpkdbx=Ye8xo4wMkyntME45xv15DeyqV32aeCAcSaa+vDpfA@mail.gmail.com> (raw)
In-Reply-To: <20131216121524.GA6177@earth.universe>

On Mon, Dec 16, 2013 at 1:15 PM, Sebastian Reichel <sre@debian.org> wrote:
> On Mon, Dec 16, 2013 at 10:48:06AM +0100, Linus Walleij wrote:

>> I.e. it doesn't look device-specific at all, just like some
>> generic glue code that could be useful to many such
>> scenarios.
>
> I like the idea.
>
> Probably the remaining gpio exporting code can be converted into
> some generic gpio-sysfs-export driver as well.

I am very reluctant in letting device trees specify exports of GPIOs
to userspace, not so much because it's Linux-specific but for
the fact that people are doing things in userspace that should not
be done in userspace.

Last time it was proposed I asked to the specific usecase,
exactly why userspace needed this handle on a physical
GPIO line, and why it can't use another userspace interface
(example: leds, keys etc.)

> What do you think about the following?
>
> /*
>  * driver, which provides generic reset notifications
>  */
> cmt_reset: reset-notifier {
>     compatible = "linux,reset-notification";
>
>     interrupts = <gpio>;
> };

Looks good to me.

> /*
>  * driver, which exports the specified gpios in sysfs with the
>  * supplied names. The device will be named according to the
>  * label
>  */
> cmt_gpios: gpio-sysfs-export {
>     compatible = "linux,gpio-sysfs-export";
>     label = "nokia-cmt";
>
>     gpios = <A>, <B>, ...;
>     gpio-names = "A", "B", ...;
> };

Please follow the discussion on this topic:
http://marc.info/?l=linux-gpio&m=138201170431416&w=2

>> Why are you using a tasklet rather than a work
>> for this?
>
> No particular reason. I just took this over from Nokia's code.

Can you try to use a work instead?

Yours,
Linus Walleij