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 5ED12C4332F for ; Wed, 12 Jan 2022 15:48:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354787AbiALPse (ORCPT ); Wed, 12 Jan 2022 10:48:34 -0500 Received: from mail-qt1-f175.google.com ([209.85.160.175]:45918 "EHLO mail-qt1-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229772AbiALPs2 (ORCPT ); Wed, 12 Jan 2022 10:48:28 -0500 Received: by mail-qt1-f175.google.com with SMTP id b14so539786qtb.12; Wed, 12 Jan 2022 07:48:27 -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=kircZLJvKwRq35Roqu4N6EMju+IOfz7v3tu0eijvuOU=; b=LEIrqV9yECq4SqBx2lMVqSMS3hTrwBX8nIEmzY6ExfuBiw8t6ehKj4TpGVuuratF+1 /BgIHAtr7MlVlmKt4Bm4I3efuRA3nsDNmWUIcI9fgpt/KuJcp6ftXsAyS9WI9VFlo0J0 Dd9JLt9NC0TUfIJoexs0uy7UcYlswSsesu/VUX3CT11HD8TFCmfvdaTGA2NXYH/7Wh4B jIFVewCLTZe9Srs3SAAweM8IktfINymd3URY0Uc64HgV7Rym3QKyrPYKKOSn40aAv+Sz y+BIJF14pS9F2EoBQ5hmafi4piheVUDwARRdPn8reWFelEMXy14yVfnQclxnRuhtj35W LU/w== X-Gm-Message-State: AOAM530u1tR6grVfDSUanJzDxJOYqd/SvYzxACkUVV+V3aLO98DDkTCS JgjPk89HIbUf+Lri+rpyuVLkiXcEYqUQQb+evKE= X-Google-Smtp-Source: ABdhPJxfYKk7N1kK4CG7HmXjc71yVz5vqxe5I1MLV5trX7z8Y3w5M287yv5s5mrOzbSUgk5scgell01Doa8kJvJe/HQ= X-Received: by 2002:a05:622a:178e:: with SMTP id s14mr61437qtk.302.1642002505776; Wed, 12 Jan 2022 07:48:25 -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> <78a17bae-435b-e35e-b2dc-1166777725a0@omp.ru> In-Reply-To: From: "Rafael J. Wysocki" Date: Wed, 12 Jan 2022 16:48:14 +0100 Message-ID: Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional To: Hans de Goede Cc: Sergey Shtylyov , "Rafael J. Wysocki" , Geert Uytterhoeven , Andrew Lunn , =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= , Ulf Hansson , Vignesh Raghavendra , KVM list , 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" , Richard Weinberger , Mun Yew Tham , 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 4:14 PM Hans de Goede wrote: > > Hi, > > On 1/12/22 16:05, Sergey Shtylyov wrote: > > On 1/12/22 5:41 PM, Rafael J. Wysocki 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. > >>>>Hi, > >>>> 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 > > > > IIRC Linus has proclaimed that IRQ0 was valid for the i8253 driver (living in > > arch/x86/); IRQ0 only was frowned upon when returned by platform_get_irq() and its > > ilk. > > > > MBR, Sergey > > Right, platform_get_irq() has this: > > WARN(ret == 0, "0 is an invalid IRQ number\n"); > > So given that platform_get_irq() returning 0 is not expected, it seems > reasonable for platform_get_irq_optional() to use 0 as a special > "no irq available" return value, matching the NULL returned by > gpiod_get_optional(). Sounds reasonable to me.