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(2001-1c00-0c1e-bf00-1db8-22d3-1bc9-8ca1.cable.dynamic.v6.ziggo.nl. [2001:1c00:c1e:bf00:1db8:22d3:1bc9:8ca1]) by smtp.gmail.com with ESMTPSA id o25sm40807edr.20.2022.01.12.07.13.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Jan 2022 07:13:55 -0800 (PST) Message-ID: Date: Wed, 12 Jan 2022 16:13:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional Content-Language: en-US To: Sergey Shtylyov , "Rafael J. Wysocki" , Geert Uytterhoeven Cc: Andrew Lunn , =?UTF-8?Q?Uwe_Kleine-K=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 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> From: Hans de Goede In-Reply-To: <78a17bae-435b-e35e-b2dc-1166777725a0@omp.ru> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(). Regards, Hans