Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9738C41535 for ; Wed, 12 Jan 2022 14:41:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354212AbiALOly (ORCPT ); Wed, 12 Jan 2022 09:41:54 -0500 Received: from mail-qt1-f173.google.com ([209.85.160.173]:42834 "EHLO mail-qt1-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354194AbiALOlv (ORCPT ); Wed, 12 Jan 2022 09:41:51 -0500 Received: by mail-qt1-f173.google.com with SMTP id y17so3182165qtx.9; Wed, 12 Jan 2022 06:41:50 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eqySNHIMSrRvIgAiOM0qBvook97PLGK990KJv8uK3eo=; b=uo5AZ07a45C8mgYze+9+LAsur76rvJV1DGpCdlYCi7UZcjbwACwzjc/eblHrNcD7BE uHNLEVRxsoeGiabwS9LkZ1ZnZMpb/65FHe3cAojrX37ZWtkZzSrscKxgMEs6/bNvr8Ms 64BtKLow+fHPHPVp1SWNDrqvFIfaf+3lM8CdnM9IuaGQcg6nDBuZ+PS5lPYIiD0qdv/k AQ+inGgdbiDLFdl466ew5JdWho0orVAIftNC8pQOxFZzHnd0yCQqZ8QpZZGfIFq6bKDO x/EKh2o3AnBByccsJ0Vue7ubwwFdR/3UeCeZkILSuLcENKFOcnZqgvQOHU3Frws1Ki+c 0u6Q== X-Gm-Message-State: AOAM533MvrA+dMe61LdDl6kh4TTdKET+EMfFwEYifStoXaPXqQo184hA iVk9xpsp8KTqgNzRXEslNIg5ijuZ3Rzo4S8t63k= X-Google-Smtp-Source: ABdhPJwkrdKkjqm85M1oqBy+x6EYsmedgIEeAb8RfpkJ1ISYwM2cxFKOOAchYagZSo08mCWlmbsTnHWauUmSmFEGXlM= X-Received: by 2002:a05:622a:178e:: with SMTP id s14mr7678497qtk.302.1641998509704; Wed, 12 Jan 2022 06:41:49 -0800 (PST) MIME-Version: 1.0 References: <20220110195449.12448-1-s.shtylyov@omp.ru> <20220110195449.12448-2-s.shtylyov@omp.ru> <20220110201014.mtajyrfcfznfhyqm@pengutronix.de> <20220112085009.dbasceh3obfok5dc@pengutronix.de> In-Reply-To: From: "Rafael J. Wysocki" Date: Wed, 12 Jan 2022 15:41:38 +0100 Message-ID: Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional To: Geert Uytterhoeven Cc: Andrew Lunn , =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= , Ulf Hansson , Vignesh Raghavendra , KVM list , "Rafael J. Wysocki" , linux-iio@vger.kernel.org, Linus Walleij , Amit Kucheria , ALSA Development Mailing List , Liam Girdwood , Guenter Roeck , Thierry Reding , MTD Maling List , Linux I2C , Miquel Raynal , linux-phy@lists.infradead.org, Jiri Slaby , "David S. Miller" , Khuong Dinh , Florian Fainelli , Matthias Schiffer , Joakim Zhang , Kamal Dasu , Lee Jones , Bartosz Golaszewski , Daniel Lezcano , Tony Luck , Kishon Vijay Abraham I , bcm-kernel-feedback-list , "open list:SERIAL DRIVERS" , Jakub Kicinski , Zhang Rui , Matthias Brugger , Platform Driver , Linux PWM List , Robert Richter , Saravanan Sekar , Corey Minyard , Linux PM list , Mauro Carvalho Chehab , John Garry , Peter Korsgaard , William Breathitt Gray , Mark Gross , "open list:GPIO SUBSYSTEM" , Alex Williamson , Mark Brown , Borislav Petkov , Eric Auger , Takashi Iwai , Jaroslav Kysela , openipmi-developer@lists.sourceforge.net, Andy Shevchenko , Benson Leung , Pengutronix Kernel Team , Linux ARM , "open list:EDAC-CORE" , Sergey Shtylyov , Richard Weinberger , Mun Yew Tham , Hans de Goede , Greg Kroah-Hartman , Yoshihiro Shimoda , Cornelia Huck , Linux MMC List , Linux Kernel Mailing List , linux-spi , Linux-Renesas , Vinod Koul , James Morse , Zha Qipeng , Sebastian Reichel , =?UTF-8?Q?Niklas_S=C3=B6derlund?= , "moderated list:ARM/Mediatek SoC..." , Brian Norris , netdev Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 12, 2022 at 2:55 PM Geert Uytterhoeven wrote: > > Hi Andrew, > > On Wed, Jan 12, 2022 at 2:38 PM Andrew Lunn wrote: > > > If an optional IRQ is not present, drivers either just ignore it (e.g. > > > for devices that can have multiple interrupts or a single muxed IRQ), > > > or they have to resort to polling. For the latter, fall-back handling > > > is needed elsewhere in the driver. > > > To me it sounds much more logical for the driver to check if an > > > optional irq is non-zero (available) or zero (not available), than to > > > sprinkle around checks for -ENXIO. In addition, you have to remember > > > that this one returns -ENXIO, while other APIs use -ENOENT or -ENOSYS > > > (or some other error code) to indicate absence. I thought not having > > > to care about the actual error code was the main reason behind the > > > introduction of the *_optional() APIs. > > > > The *_optional() functions return an error code if there has been a > > real error which should be reported up the call stack. This excludes > > whatever error code indicates the requested resource does not exist, > > which can be -ENODEV etc. If the device does not exist, a magic cookie > > is returned which appears to be a valid resources but in fact is > > not. So the users of these functions just need to check for an error > > code, and fail the probe if present. > > Agreed. > > Note that in most (all?) other cases, the return type is a pointer > (e.g. to struct clk), and NULL is the magic cookie. > > > You seems to be suggesting in binary return value: non-zero > > (available) or zero (not available) > > Only in case of success. In case of a real failure, an error code > must be returned. > > > This discards the error code when something goes wrong. That is useful > > information to have, so we should not be discarding it. > > No, the error code must be retained in case of failure. > > > IRQ don't currently have a magic cookie value. One option would be to > > add such a magic cookie to the subsystem. Otherwise, since 0 is > > invalid, return 0 to indicate the IRQ does not exist. > > Exactly. And using 0 means the similar code can be used as for other > subsystems, where NULL would be returned. > > The only remaining difference is the "dummy cookie can be passed > to other functions" behavior. Which is IMHO a valid difference, > as unlike with e.g. clk_prepare_enable(), you do pass extra data to > request_irq(), and sometimes you do need to handle the absence of > the interrupt using e.g. polling. > > > The request for a script checking this then makes sense. However, i > > don't know how well coccinelle/sparse can track values across function > > calls. They probably can check for: > > > > ret = irq_get_optional() > > if (ret < 0) > > return ret; > > > > A missing if < 0 statement somewhere later is very likely to be an > > error. A comparison of <= 0 is also likely to be an error. A check for > > > 0 before calling any other IRQ functions would be good. I'm > > surprised such a check does not already existing in the IRQ API, but > > there are probably historical reasons for that. > > There are still a few platforms where IRQ 0 does exist. Not just a few even. This happens on a reasonably recent x86 PC: rafael@gratch:~/work/linux-pm> head -2 /proc/interrupts CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 0: 10 0 0 0 0 0 IR-IO-APIC 2-edge timer