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

From: Sebastian Reichel <sre@ring0.de>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: "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 19:34:50 +0100	[thread overview]
Message-ID: <20131216183448.GA10614@earth.universe> (raw)
In-Reply-To: <CACRpkdbx=Ye8xo4wMkyntME45xv15DeyqV32aeCAcSaa+vDpfA@mail.gmail.com>

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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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