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Date: Wed, 12 Jan 2022 16:48:14 +0100 From: "Rafael J. Wysocki" <rafael@...nel.org> To: Hans de Goede <hdegoede@...hat.com> Cc: Sergey Shtylyov <s.shtylyov@....ru>, "Rafael J. Wysocki" <rafael@...nel.org>, Geert Uytterhoeven <geert@...ux-m68k.org>, Andrew Lunn <andrew@...n.ch>, Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, Ulf Hansson <ulf.hansson@...aro.org>, Vignesh Raghavendra <vigneshr@...com>, KVM list <kvm@...r.kernel.org>, linux-iio@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>, Amit Kucheria <amitk@...nel.org>, ALSA Development Mailing List <alsa-devel@...a-project.org>, Liam Girdwood <lgirdwood@...il.com>, Guenter Roeck <groeck@...omium.org>, Thierry Reding <thierry.reding@...il.com>, MTD Maling List <linux-mtd@...ts.infradead.org>, Linux I2C <linux-i2c@...r.kernel.org>, Miquel Raynal <miquel.raynal@...tlin.com>, linux-phy@...ts.infradead.org, Jiri Slaby <jirislaby@...nel.org>, "David S. Miller" <davem@...emloft.net>, Khuong Dinh <khuong@...amperecomputing.com>, Florian Fainelli <f.fainelli@...il.com>, Matthias Schiffer <matthias.schiffer@...tq-group.com>, Joakim Zhang <qiangqing.zhang@....com>, Kamal Dasu <kdasu.kdev@...il.com>, Lee Jones <lee.jones@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, Daniel Lezcano <daniel.lezcano@...aro.org>, Tony Luck <tony.luck@...el.com>, Kishon Vijay Abraham I <kishon@...com>, bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>, "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>, Jakub Kicinski <kuba@...nel.org>, Zhang Rui <rui.zhang@...el.com>, Matthias Brugger <matthias.bgg@...il.com>, Platform Driver <platform-driver-x86@...r.kernel.org>, Linux PWM List <linux-pwm@...r.kernel.org>, Robert Richter <rric@...nel.org>, Saravanan Sekar <sravanhome@...il.com>, Corey Minyard <minyard@....org>, Linux PM list <linux-pm@...r.kernel.org>, Mauro Carvalho Chehab <mchehab@...nel.org>, John Garry <john.garry@...wei.com>, Peter Korsgaard <peter@...sgaard.com>, William Breathitt Gray <vilhelm.gray@...il.com>, Mark Gross <markgross@...nel.org>, "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>, Alex Williamson <alex.williamson@...hat.com>, Mark Brown <broonie@...nel.org>, Borislav Petkov <bp@...en8.de>, Eric Auger <eric.auger@...hat.com>, Takashi Iwai <tiwai@...e.com>, Jaroslav Kysela <perex@...ex.cz>, openipmi-developer@...ts.sourceforge.net, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Benson Leung <bleung@...omium.org>, Pengutronix Kernel Team <kernel@...gutronix.de>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, "open list:EDAC-CORE" <linux-edac@...r.kernel.org>, Richard Weinberger <richard@....at>, Mun Yew Tham <mun.yew.tham@...el.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, Cornelia Huck <cohuck@...hat.com>, Linux MMC List <linux-mmc@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-spi <linux-spi@...r.kernel.org>, Linux-Renesas <linux-renesas-soc@...r.kernel.org>, Vinod Koul <vkoul@...nel.org>, James Morse <james.morse@....com>, Zha Qipeng <qipeng.zha@...el.com>, Sebastian Reichel <sre@...nel.org>, Niklas Söderlund <niklas.soderlund@...natech.se>, "moderated list:ARM/Mediatek SoC..." <linux-mediatek@...ts.infradead.org>, Brian Norris <computersforpeace@...il.com>, netdev <netdev@...r.kernel.org> Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional On Wed, Jan 12, 2022 at 4:14 PM Hans de Goede <hdegoede@...hat.com> 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@...tch:~/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.
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