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 825F4C433F5 for ; Wed, 12 Jan 2022 15:05:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354434AbiALPFh (ORCPT ); Wed, 12 Jan 2022 10:05:37 -0500 Received: from mxout01.lancloud.ru ([45.84.86.81]:48906 "EHLO mxout01.lancloud.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348019AbiALPFf (ORCPT ); Wed, 12 Jan 2022 10:05:35 -0500 Received: from LanCloud DKIM-Filter: OpenDKIM Filter v2.11.0 mxout01.lancloud.ru ED05520DDDAB Received: from LanCloud Received: from LanCloud Received: from LanCloud Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional To: "Rafael J. Wysocki" , Geert Uytterhoeven CC: Andrew Lunn , =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Ulf Hansson , Vignesh Raghavendra , KVM list , , Linus Walleij , "Amit Kucheria" , ALSA Development Mailing List , Liam Girdwood , "Guenter Roeck" , Thierry Reding , "MTD Maling List" , Linux I2C , Miquel Raynal , , 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 , , Andy Shevchenko , Benson Leung , Pengutronix Kernel Team , Linux ARM , "open list:EDAC-CORE" , 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 References: <20220110195449.12448-1-s.shtylyov@omp.ru> <20220110195449.12448-2-s.shtylyov@omp.ru> <20220110201014.mtajyrfcfznfhyqm@pengutronix.de> <20220112085009.dbasceh3obfok5dc@pengutronix.de> From: Sergey Shtylyov Organization: Open Mobile Platform Message-ID: <78a17bae-435b-e35e-b2dc-1166777725a0@omp.ru> Date: Wed, 12 Jan 2022 18:05:24 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.11.198] X-ClientProxiedBy: LFEXT01.lancloud.ru (fd00:f066::141) To LFEX1907.lancloud.ru (fd00:f066::207) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. >>> >>> 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