From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04F68C43387 for ; Mon, 17 Dec 2018 07:53:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D07852084D for ; Mon, 17 Dec 2018 07:53:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731517AbeLQHxg (ORCPT ); Mon, 17 Dec 2018 02:53:36 -0500 Received: from metis.ext.pengutronix.de ([85.220.165.71]:34517 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726349AbeLQHxf (ORCPT ); Mon, 17 Dec 2018 02:53:35 -0500 Received: from ptx.hi.pengutronix.de ([2001:67c:670:100:1d::c0]) by metis.ext.pengutronix.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1gYniN-0000bW-FO; Mon, 17 Dec 2018 08:53:23 +0100 Received: from ukl by ptx.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1gYniL-0000uu-UU; Mon, 17 Dec 2018 08:53:21 +0100 Date: Mon, 17 Dec 2018 08:53:21 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Paul Cercueil Cc: Linus Walleij , "thierry.reding@gmail.com" , 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: <20181217075321.k45vhgnszeqs3tea@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> <20181214142628.zwi4hadrju53z6f3@pengutronix.de> <1544969932.1649.1@crapouillou.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1544969932.1649.1@crapouillou.net> User-Agent: NeoMutt/20170113 (1.7.2) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-mips@vger.kernel.org Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Sun, Dec 16, 2018 at 03:18:52PM +0100, Paul Cercueil wrote: > Hi, > > Le ven. 14 déc. 2018 ŕ 15:26, Uwe Kleine-König > a écrit : > > 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? > > If we're going to do something like this, should it be the drivers or > the core (within pwmchip_add) that checks for this "npwms" property? Of course this should be done in the core. The driver than can rely on the validity of the index. But as I wrote before, this shouldn't stop your patch from going in. But if Thierry agrees that this npmws (or num-pwms) is a good idea, it would be great to start early to convert drivers. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |