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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 0F7F8C43387 for ; Sun, 16 Dec 2018 14:19:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ADD14217F9 for ; Sun, 16 Dec 2018 14:19:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=crapouillou.net header.i=@crapouillou.net header.b="kpCkiwt8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730518AbeLPOTC (ORCPT ); Sun, 16 Dec 2018 09:19:02 -0500 Received: from outils.crapouillou.net ([89.234.176.41]:47650 "EHLO crapouillou.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730181AbeLPOTC (ORCPT ); Sun, 16 Dec 2018 09:19:02 -0500 Date: Sun, 16 Dec 2018 15:18:52 +0100 From: Paul Cercueil Subject: Re: [PATCH v8 15/26] pwm: jz4740: Add support for the JZ4725B To: Uwe =?iso-8859-1?q?Kleine-K=F6nig?= 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 Message-Id: <1544969932.1649.1@crapouillou.net> In-Reply-To: <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> <20181214142628.zwi4hadrju53z6f3@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1544969939; bh=Hq0ZCESR3VxDldevdsZM7ZBAIOVzdtDgctxCR8ptZxw=; h=Date:From:Subject:To:Cc:Message-Id:In-Reply-To:References:MIME-Version:Content-Type:Content-Transfer-Encoding; b=kpCkiwt8CzWBqSxf3PO2XKz2pv714bSG/ju7bnOTcthGFgwwX/s/S89ZPxETnVvQu+mZCgmWYFY/fYruHETa+6BD01b8ZDJoHAl0etWfET5yqAvlsF9V1BKhn0PsicOtXTS7sRSzuHiJO2hVto2EJlpt1+mUmFAL75SX6rs40j4= Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi, Le ven. 14 d=E9c. 2018 =E0 15:26, Uwe Kleine-K=F6nig=20 a =E9crit : > Hello, >=20 > On Fri, Dec 14, 2018 at 02:50:20PM +0100, Linus Walleij wrote: >> On Thu, Dec 13, 2018 at 9:42 PM Uwe Kleine-K=F6nig >> wrote: >> > [Adding Linus Walleij to Cc:] >> > On Thu, Dec 13, 2018 at 03:03:15PM +0100, Paul Cercueil wrote: >> > > Le jeu. 13 d=E9c. 2018 =E0 10:24, Uwe Kleine-K=F6nig >> > > a =E9crit : >> > > > 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,=20 >> except that >> > > > > it >> > > > > only has 6 channels available instead of 8. >> > > > >> > > > this driver is probed only from device tree? If yes, it might=20 >> be >> > > > sensible to specify the number of PWMs there and get it from=20 >> there. >> > > > There doesn't seem to be a generic binding for that, but=20 >> there are >> > > > several drivers that could benefit from it. (This is a bigger=20 >> project >> > > > though and shouldn't stop your patch. Still more as it=20 >> already got >> > > > Thierry's ack.) >> > > >> > > I think there needs to be a proper guideline, as there doesn't=20 >> seem to be >> > > a consensus about this. I learned from emails with Rob and=20 >> Linus (Walleij) >> > > that I should not have in devicetree what I can deduce from the=20 >> compatible >> > > string. >> > >> > I understood them a bit differently. It is ok to deduce things=20 >> from the >> > compatible string. But if you define a generic property (say)=20 >> "num-pwms" >> > that is used uniformly in most bindings this is ok, too. (And=20 >> then the >> > two different devices could use the same compatible.) >> > >> > An upside of the generic "num-pwms" property is that the pwm core=20 >> could >> > sanity check pwm phandles before passing them to the hardware=20 >> drivers. >>=20 >> 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. >>=20 >> 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. >>=20 >> 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. >=20 > This looks very similar to the case under discussion. >=20 >> So if the PWM case is something similar, then by all means add >> num-pwms. >=20 > .. 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? > Best regards > Uwe >=20 > -- > Pengutronix e.K. | Uwe Kleine-K=F6nig =20 > | > Industrial Linux Solutions |=20 > http://www.pengutronix.de/ | =