From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Hunter Subject: Re: [PATCH 3/5] gpio/omap: Add DT support to GPIO driver Date: Tue, 16 Apr 2013 18:14:21 -0500 Message-ID: <516DDB4D.9020500@ti.com> References: <1329321854-24490-1-git-send-email-b-cousson@ti.com> <514C79E1.4090106@wwwdotorg.org> <514CE0AB.6060207@ti.com> <515319D5.20105@wwwdotorg.org> <5155C902.7080207@wwwdotorg.org> <5165CB9D.1090202@wwwdotorg.org> <51671D7B.5060303@wwwdotorg.org> <51673D70.3010503@wwwdotorg.org> <516C31C3.9040505@wwwdotorg.or g> <516C73C6.5050409@ti.co m> <516C7C43.3040105@wwwdotorg.org> <516C8760.2050500@ti.com> <516D9B05.1000501@wwwdotorg.org> <516DA60A.5070000@ti.com> <516DCCA8.3070108@wwwdotorg.org> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <516DCCA8.3070108@wwwdotorg.org> Sender: linux-omap-owner@vger.kernel.org To: Stephen Warren Cc: Linus Walleij , Javier Martinez Canillas , Grant Likely , Alexandre Courbot , Stephen Warren , Kevin Hilman , "devicetree-discuss@lists.ozlabs.org" , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" List-Id: devicetree@vger.kernel.org On 04/16/2013 05:11 PM, Stephen Warren wrote: > On 04/16/2013 01:27 PM, Jon Hunter wrote: >> >> On 04/16/2013 01:40 PM, Stephen Warren wrote: >>> On 04/15/2013 05:04 PM, Jon Hunter wrote: > ... >>>> If some driver is calling gpio_request() directly, then they will most >>>> likely just call gpio_to_irq() when requesting the interrupt and so the >>>> xlate function would not be called in this case (mmc drivers are a good >>>> example). So I don't see that as being a problem. In fact that's the >>>> benefit of this approach as AFAICT it solves this problem. >>> >>> Oh. That assumption seems very fragile. What about drivers that actually >>> do have platform data (or DT bindings) that provide both the IRQ and >>> GPIO IDs, and hence don't use gpio_to_irq()? That's entirely possible. >> >> Right. In the DT case though, if someone does provide the IRQ and GPIO >> IDs then at least they would use a different xlate function. Another >> option to consider would be defining the #interrupt-cells = <3> where we >> would have ... >> >> cell-#1 --> IRQ domain ID >> cell-#2 --> Trigger type >> cell-#3 --> GPIO ID >> >> Then we could have a generic xlate for 3 cells that would also request >> the GPIO. Again not sure if people are against a gpio being requested in >> the xlate but just an idea. Or given that irq_of_parse_and_map() calls >> the xlate, we could have this function call gpio_request() if the >> interrupt controller is a gpio and there are 3 cells. > > I rather dislike this approach since: > > a) It requires changes to the DT bindings, which are already defined. > Admittedly it's backwards-compatible, but still. > > b) There isn't really any need for the DT to represent this; the > GPIO+IRQ driver itself already knows which IRQ ID is which GPIO ID and > vice-versa (if the HW has such a concept), so there's no need for the DT > to contain this information. This seems like pushing Linux's internal > requirements into the design of the DT binding. Yes, so the only alternative is to use irq_to_gpio to avoid this. > c) I have the feeling that hooking the of_xlate function for this is a > bit of an abuse of the function. I was wondering about that. So I was grep'ing through the various xlate implementations and found this [1]. Also you may recall that in the of_dma_simple_xlate() we call the dma_request_channel() to allocate the channel, which is very similar. However, I don't wish to get a reputation as abusing APIs so would be good to know if this really is abuse or not ;-) Cheers Jon [1] http://permalink.gmane.org/gmane.linux.ports.arm.kernel/195124