From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from metis.ext.pengutronix.de ([85.220.165.71]:41545 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730138AbeLNO0p (ORCPT ); Fri, 14 Dec 2018 09:26:45 -0500 Date: Fri, 14 Dec 2018 15:26:28 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Linus Walleij , "thierry.reding@gmail.com" Cc: Paul Cercueil , Rob Herring , Mark Rutland , Daniel Lezcano , Thomas Gleixner , Ralf Baechle , paul.burton@mips.com, James Hogan , Jonathan Corbet , Mathieu Malaterre , ezequiel@collabora.co.uk, prasannatsmkumar@gmail.com, linux-pwm@vger.kernel.org, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , "linux-kernel@vger.kernel.org" , LINUXWATCHDOG , linux-mips@vger.kernel.org, linux-doc@vger.kernel.org, linux-clk , od@zcrc.me Subject: Re: [PATCH v8 15/26] pwm: jz4740: Add support for the JZ4725B Message-ID: <20181214142628.zwi4hadrju53z6f3@pengutronix.de> References: <20181212220922.18759-1-paul@crapouillou.net> <20181212220922.18759-16-paul@crapouillou.net> <20181213092409.ml4wpnzow2nnszkd@pengutronix.de> <1544709795.18952.1@crapouillou.net> <20181213204219.onem3q6dcmakusl2@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-watchdog-owner@vger.kernel.org List-Id: linux-watchdog@vger.kernel.org Hello, On Fri, Dec 14, 2018 at 02:50:20PM +0100, Linus Walleij wrote: > On Thu, Dec 13, 2018 at 9:42 PM Uwe Kleine-König > wrote: > > [Adding Linus Walleij to Cc:] > > On Thu, Dec 13, 2018 at 03:03:15PM +0100, Paul Cercueil wrote: > > > Le jeu. 13 déc. 2018 ŕ 10:24, Uwe Kleine-König > > > a écrit : > > > > On Wed, Dec 12, 2018 at 11:09:10PM +0100, Paul Cercueil wrote: > > > > > The PWM in the JZ4725B works the same as in the JZ4740, except that > > > > > it > > > > > only has 6 channels available instead of 8. > > > > > > > > this driver is probed only from device tree? If yes, it might be > > > > sensible to specify the number of PWMs there and get it from there. > > > > There doesn't seem to be a generic binding for that, but there are > > > > several drivers that could benefit from it. (This is a bigger project > > > > though and shouldn't stop your patch. Still more as it already got > > > > Thierry's ack.) > > > > > > I think there needs to be a proper guideline, as there doesn't seem to be > > > a consensus about this. I learned from emails with Rob and Linus (Walleij) > > > that I should not have in devicetree what I can deduce from the compatible > > > string. > > > > I understood them a bit differently. It is ok to deduce things from the > > compatible string. But if you define a generic property (say) "num-pwms" > > that is used uniformly in most bindings this is ok, too. (And then the > > two different devices could use the same compatible.) > > > > An upside of the generic "num-pwms" property is that the pwm core could > > sanity check pwm phandles before passing them to the hardware drivers. > > I don't know if this helps, but in GPIO we have "ngpios" which is > used to augment an existing block as to the number of lines actually > used with it. > > The typical case is that an ASIC engineer synthesize a block for > 32 GPIOs but only 12 of them are routed to external pads. So > we augment the behaviour of that driver to only use 12 of the > 32 lines. > > I guess using the remaining 20 lines "works" in a sense but they > have no practical use and will just bias electrons in the silicon > for no use. This looks very similar to the case under discussion. > So if the PWM case is something similar, then by all means add > num-pwms. .. or "npwms" to use the same nomenclature as the gpio binding? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |