Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional
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- Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional
- From: Sergey Shtylyov <s.shtylyov@xxxxxx>
- Date: Wed, 19 Jan 2022 19:12:23 +0300
- Cc: Andrew Lunn <andrew@xxxxxxx>, Ulf Hansson <ulf.hansson@xxxxxxxxxx>, Vignesh Raghavendra <vigneshr@xxxxxx>, KVM list <kvm@xxxxxxxxxxxxxxx>, "Rafael J. Wysocki" <rafael@xxxxxxxxxx>, <linux-iio@xxxxxxxxxxxxxxx>, "Linus Walleij" <linus.walleij@xxxxxxxxxx>, Amit Kucheria <amitk@xxxxxxxxxx>, "ALSA Development Mailing List" <alsa-devel@xxxxxxxxxxxxxxxx>, Jaroslav Kysela <perex@xxxxxxxx>, Guenter Roeck <groeck@xxxxxxxxxxxx>, Thierry Reding <thierry.reding@xxxxxxxxx>, MTD Maling List <linux-mtd@xxxxxxxxxxxxxxxxxxx>, Linux I2C <linux-i2c@xxxxxxxxxxxxxxx>, Miquel Raynal <miquel.raynal@xxxxxxxxxxx>, <linux-phy@xxxxxxxxxxxxxxxxxxx>, linux-spi <linux-spi@xxxxxxxxxxxxxxx>, Jiri Slaby <jirislaby@xxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, Khuong Dinh <khuong@xxxxxxxxxxxxxxxxxxxxxx>, Florian Fainelli <f.fainelli@xxxxxxxxx>, Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>, Kamal Dasu <kdasu.kdev@xxxxxxxxx>, "Greg Kroah-Hartman" <gregkh@xxxxxxxxxxxxxxxxxxx>, Lee Jones <lee.jones@xxxxxxxxxx>, Bartosz Golaszewski <brgl@xxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>, Kishon Vijay Abraham I <kishon@xxxxxx>, bcm-kernel-feedback-list <bcm-kernel-feedback-list@xxxxxxxxxxxx>, "open list:SERIAL DRIVERS" <linux-serial@xxxxxxxxxxxxxxx>, Jakub Kicinski <kuba@xxxxxxxxxx>, Zhang Rui <rui.zhang@xxxxxxxxx>, <platform-driver-x86@xxxxxxxxxxxxxxx>, Linux PWM List <linux-pwm@xxxxxxxxxxxxxxx>, Robert Richter <rric@xxxxxxxxxx>, "Saravanan Sekar" <sravanhome@xxxxxxxxx>, Corey Minyard <minyard@xxxxxxx>, Linux PM list <linux-pm@xxxxxxxxxxxxxxx>, Liam Girdwood <lgirdwood@xxxxxxxxx>, "Mauro Carvalho Chehab" <mchehab@xxxxxxxxxx>, John Garry <john.garry@xxxxxxxxxx>, Peter Korsgaard <peter@xxxxxxxxxxxxx>, William Breathitt Gray <vilhelm.gray@xxxxxxxxx>, Mark Gross <markgross@xxxxxxxxxx>, Hans de Goede <hdegoede@xxxxxxxxxx>, Alex Williamson <alex.williamson@xxxxxxxxxx>, "Mark Brown" <broonie@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Takashi Iwai <tiwai@xxxxxxxx>, Matthias Brugger <matthias.bgg@xxxxxxxxx>, <openipmi-developer@xxxxxxxxxxxxxxxxxxxxx>, Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>, Benson Leung <bleung@xxxxxxxxxxxx>, Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx>, Linux ARM <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, <linux-edac@xxxxxxxxxxxxxxx>, "Tony Luck" <tony.luck@xxxxxxxxx>, Richard Weinberger <richard@xxxxxx>, Mun Yew Tham <mun.yew.tham@xxxxxxxxx>, Eric Auger <eric.auger@xxxxxxxxxx>, netdev <netdev@xxxxxxxxxxxxxxx>, "open list:GPIO SUBSYSTEM" <linux-gpio@xxxxxxxxxxxxxxx>, Cornelia Huck <cohuck@xxxxxxxxxx>, "Linux MMC List" <linux-mmc@xxxxxxxxxxxxxxx>, Joakim Zhang <qiangqing.zhang@xxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Linux-Renesas <linux-renesas-soc@xxxxxxxxxxxxxxx>, Vinod Koul <vkoul@xxxxxxxxxx>, "James Morse" <james.morse@xxxxxxx>, Zha Qipeng <qipeng.zha@xxxxxxxxx>, "Sebastian Reichel" <sre@xxxxxxxxxx>, Niklas Söderlund <niklas.soderlund@xxxxxxxxxxxx>, <linux-mediatek@xxxxxxxxxxxxxxxxxxx>, "Brian Norris" <computersforpeace@xxxxxxxxx>, Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
- In-reply-to: <20220118142945.6y3rmvzt44pjpr4z@pengutronix.de>
- Organization: Open Mobile Platform
- References: <20220117092444.opoedfcf5k5u6otq@pengutronix.de> <CAMuHMdUgZUeraHadRAi2Z=DV+NuNBrKPkmAKsvFvir2MuquVoA@mail.gmail.com> <20220117114923.d5vajgitxneec7j7@pengutronix.de> <CAMuHMdWCKERO20R2iVHq8P=BaoauoBAtiampWzfMRYihi3Sb0g@mail.gmail.com> <20220117170609.yxaamvqdkivs56ju@pengutronix.de> <CAMuHMdXbuZqEpYivyS6hkaRN+CwTOGaHq_OROwVAWvDD6OXODQ@mail.gmail.com> <20220118090913.pjumkq4zf4iqtlha@pengutronix.de> <CAMuHMdUW8+Y_=uszD+JOZO3Lpa9oDayk+GO+cg276i2f2T285w@mail.gmail.com> <20220118120806.pbjsat4ulg3vnhsh@pengutronix.de> <CAMuHMdWkwV9XE_R5FZ=jPtDwLpDbEngG6+X2JmiDJCZJZvUjYA@mail.gmail.com> <20220118142945.6y3rmvzt44pjpr4z@pengutronix.de>
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On 1/18/22 5:29 PM, Uwe Kleine-König wrote:
>> nst the magic not-found value (so no implementation detail magic
>>>>> leaks into the caller code) and just pass it to the next API function=
>> .
>>>>> (And my expectation would be that if you chose to represent not-found=
>> by
>>>>> (void *)66 instead of NULL, you won't have to adapt any user, just th=
>> e
>>>>> framework internal checks. This is a good thing!)
>>>>
>>>> Ah, there is the wrong assumption: drivers sometimes do need to know
>>>> if the resource was found, and thus do need to know about (void *)66,
>>>> -ENODEV, or -ENXIO. I already gave examples for IRQ and clk before.
>>>> I can imagine these exist for gpiod and regulator, too, as soon as
>>>> you go beyond the trivial "enable" and "disable" use-cases.
>>>
>>> My premise is that every user who has to check for "not found"
>>> explicitly should not use (clk|gpiod)_get_optional() but
>>> (clk|gpiod)_get() and do proper (and explicit) error handling for
>>> -ENODEV. (clk|gpiod)_get_optional() is only for these trivial use-cases.
>>>
>>>> And 0/NULL vs. > 0 is the natural check here: missing, but not
>>>> an error.
>>>
>>> For me it it 100% irrelevant if "not found" is an error for the query
>>> function or not. I just have to be able to check for "not found" and
>>> react accordingly.
>>>
>>> And adding a function
>>>
>>> def platform_get_irq_opional():
>>> ret =3D platform_get_irq()
>>> if ret =3D=3D -ENXIO:
>>> return 0
>>> return ret
>>>
>>> it's not a useful addition to the API if I cannot use 0 as a dummy
>>> because it doesn't simplify the caller enough to justify the additional
>>> function.
>>>
>>> The only thing I need to be able is to distinguish the cases "there is
>>> an irq", "there is no irq" and anything else is "there is a problem I
>>> cannot handle and so forward it to my caller". The semantic of
>>> platform_get_irq() is able to satisfy this requirement[1], so why introdu=
>> ce
>>> platform_get_irq_opional() for the small advantage that I can check for
>>> not-found using
>>>
>>> if (!irq)
>>>
>>> instead of
>>>
>>> if (irq !=3D -ENXIO)
>>>
>>> ? The semantic of platform_get_irq() is easier ("Either a usable
>>> non-negative irq number or a negative error number") compared to
>>> platform_get_irq_optional() ("Either a usable positive irq number or a
>>> negative error number or 0 meaning not found"). Usage of
>>> platform_get_irq() isn't harder or more expensive (neither for a human
>>> reader nor for a maching running the resulting compiled code).
>>> For a human reader
>>>
>>> if (irq !=3D -ENXIO)
>>>
>>> is even easier to understand because for
>>>
>>> if (!irq)
>>>
>>> they have to check where the value comes from, see it's
>>> platform_get_irq_optional() and understand that 0 means not-found.
>>
>> "vIRQ zero does not exist."
>
> With that statement in mind I would expect that a function that gives me
> an (v)irq number never returns 0.
>
>>> This function just adds overhead because as a irq framework user I have
>>> to understand another function. For me the added benefit is too small to
>>> justify the additional function. And you break out-of-tree drivers.
>>> These are all no major counter arguments, but as the advantage isn't
>>> major either, they still matter.
>>>
>>> Best regards
>>> Uwe
>>>
>>> [1] the only annoying thing is the error message.
>>
>> So there's still a need for two functions.
>
> Or a single function not emitting an error message together with the
> callers being responsible for calling dev_err().
>
> So the options in my preference order (first is best) are:
>
> - Remove the printk from platform_get_irq() and remove
> platform_get_irq_optional();
Strong NAK here:
- dev_err() in our function saves a lot of (repeatable!) comments;
- we've already discussed that it's more optimal to check againt 0 than
against -ENXIO in the callers.
> - Rename platform_get_irq_optional() to platform_get_irq_silently()
NAK as well. We'd better off complaining about irq < 0 in this function.
> - Keep platform_get_irq_optional() as is
NAK, it's suboptimal in the call sites.
> - Collect underpants
>
> - ?
You're on your own here. :-)
> - Change semantic of platform_get_irq_optional()
Yes, we should change the semantics if it serves our goals better.
> Best regards
> Uwe
MBR, Sergey
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