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Date:   Tue, 18 Jan 2022 15:29:45 +0100
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
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Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional
Message-ID: <20220118142945.6y3rmvzt44pjpr4z@pengutronix.de>
References: <20220117092444.opoedfcf5k5u6otq@pengutronix.de>
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 <20220118090913.pjumkq4zf4iqtlha@pengutronix.de>
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On Tue, Jan 18, 2022 at 01:49:15PM +0100, Geert Uytterhoeven 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 functi=
on=3D
> .
> > > > (And my expectation would be that if you chose to represent not-fou=
nd=3D
>  by
> > > > (void *)66 instead of NULL, you won't have to adapt any user, just =
th=3D
> 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 =3D3D platform_get_irq()
> >                 if ret =3D3D=3D3D -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 intro=
du=3D
> ce
> > platform_get_irq_opional() for the small advantage that I can check for
> > not-found using
> >
> >         if (!irq)
> >
> > instead of
> >
> >         if (irq !=3D3D -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 !=3D3D -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.
>=20
> "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.
>=20
> 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();

 - Rename platform_get_irq_optional() to platform_get_irq_silently()

 - Keep platform_get_irq_optional() as is

 - Collect underpants

 - ?

 - Change semantic of platform_get_irq_optional()

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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