From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sascha Hauer Subject: Re: [PATCH v3 03/10] of: Add PWM support. Date: Sat, 25 Feb 2012 13:33:57 +0100 Message-ID: <20120225123357.GU3852@pengutronix.de> References: <1329923841-32017-1-git-send-email-thierry.reding@avionic-design.de> <201202231403.01614.arnd@arndb.de> <20120224064749.GB18786@avionic-0098.mockup.avionic-design.de> <201202241658.32062.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <201202241658.32062.arnd-r2nGTMty4D4@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann Cc: Thierry Reding , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Matthias Kaehlcke , Kurt Van Dijck , Rob Herring , Grant Likely , Colin Cross , Olof Johansson , Richard Purdie , Mark Brown , Mitch Bradley , Mike Frysinger , Eric Miao , Lars-Peter Clausen , Ryan Mallon List-Id: devicetree@vger.kernel.org On Fri, Feb 24, 2012 at 04:58:31PM +0000, Arnd Bergmann wrote: > On Friday 24 February 2012, Thierry Reding wrote: > > * Arnd Bergmann wrote: > > > On Thursday 23 February 2012, Thierry Reding wrote: > > > > * Arnd Bergmann wrote: > > > [...] > > > > > * Why not include the pwm_request() call in this and return the > > > > > pwm_device directly? You said that you want to get rid of the > > > > > pwm_id eventually, which is a good idea, but this interface still > > > > > forces one to use it. > > > > > > > > Okay, that sounds sensible. I propose to rename the function to something like > > > > of_request_pwm(). > > > > > > Sounds good. > > On second thought, I would actually prefer starting the name with pwm_ and > making it independent of device tree. There might be other ways how to > find the pwm_device from a struct device in the future, but it should always > be possible using a device together with a string and/or numeric identifier, > much in the same way that we can get a resource from a platform_device. > > Ideally, there would be a common theme behind finding a memory region, > irq, gpio pin, clock, regulator, dma-channel and pwm or anything else > that requires a link between two device nodes. > > > > > It would of course need an additional parameter (name) to > > > > forward to pwm_request(). > > > > > > Not necessarily, it could use the dev_name(device) or the name > > > of the property, or a combination of the two. > > > > The problem with that is that usually the device would be named something > > generic like "pwm", while in case where the PWM is used for the backlight > > it makes sense to label the PWM device "backlight". > > > > Looking at debugfs and seeing an entry "backlight" is much more straight- > > forward than "pwm.0". I mean "pwm.0" doesn't carry any useful information > > really, does it? > > But the device name would be from the device using the pwm, not the > pwm controller, so it should be something more helpful, no? > > > > > > > +EXPORT_SYMBOL(of_get_named_pwm); > > > > > > > > > > EXPORT_SYMBOL_GPL? > > > > > > > > It was brought up at some point that it might be nice to allow non-GPL > > > > drivers to use the PWM framework as well. I don't remember any discussion > > > > resulting from the comment. Perhaps we should have that discussion now and > > > > decide whether or not we want to keep it GPL-only or not. > > > > > > I would definitely use EXPORT_SYMBOL_GPL for all new code unless it > > > replaces an earlier interface that was available as EXPORT_SYMBOL. > > > > I just grepped the code and noticed this: > > > > $ $ git grep -n 'EXPORT_SYMBOL.*(pwm_request)' > > arch/arm/mach-vt8500/pwm.c:139:EXPORT_SYMBOL(pwm_request); > > arch/arm/plat-mxc/pwm.c:183:EXPORT_SYMBOL(pwm_request); > > arch/arm/plat-samsung/pwm.c:83:EXPORT_SYMBOL(pwm_request); > > arch/unicore32/kernel/pwm.c:132:EXPORT_SYMBOL(pwm_request); > > drivers/mfd/twl6030-pwm.c:156:EXPORT_SYMBOL(pwm_request); > > drivers/misc/ab8500-pwm.c:108:EXPORT_SYMBOL(pwm_request); > > drivers/pwm/core.c:262:EXPORT_SYMBOL_GPL(pwm_request); > > > > It seems like the legacy PWM API used to be non-GPL. Should I switch it back? > > Also does it make sense to have something like of_request_pwm() GPL when the > > rest of the API isn't? > > I guess the choice is to make between you and Sascha. The implementation is > new, so you could pick EXPORT_SYMBOL_GPL, but you could also try to > keep to the current API. I tend to use _GPL, but I have no strong objection using the non GPL variant. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |