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

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Message-ID: <20131216183448.GA10614@earth.universe>
Date:	Mon, 16 Dec 2013 19:34:50 +0100
From:	Sebastian Reichel <sre@...g0.de>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Shubhrajyoti Datta <omaplinuxkernel@...il.com>,
	Carlos Chinea <cch.devel@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Benoît Cousson <bcousson@...libre.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	Pali Rohár <pali.rohar@...il.com>,
	Ивайло Димитров 
	<freemangordon@....bg>,
	Joni Lapilainen <joni.lapilainen@...il.com>,
	Aaro Koskinen <aaro.koskinen@....fi>
Subject: Re: [RFCv4 06/11] misc: Introduce Nokia CMT driver

Hi,

On Mon, Dec 16, 2013 at 02:31:53PM +0100, Linus Walleij wrote:
> 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.)

There are a couple of lines ("cmt_apeslpx", "cmt_rst_rq", "cmt_en",
"cmt_rst", "cmt_bsi"), which are handled by ofono to do the correct
power sequence for the modem. The relevant ofono code is here:

https://git.kernel.org/cgit/network/ofono/ofono.git/tree/plugins/nokia-gpio.c

In MeeGo etc. they have a little board specific init script, which
exports the gpio lines and setups some symlinks. IMHO at least the
board specific stuff should be handled by the kernel, thus I added
this code to the driver. I guess you prefer to move the power
sequencing completly to the kernel?

> > 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.

Ok :) I will prepare something for the next patch.

> > /*
> >  * 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

Ok.

> >> 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?

Yes. I will have a look at this.

-- Sebastian

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