netdev - Re: [PATCH 1/2] platform: make platform_get_irq

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Date:   Tue, 18 Jan 2022 09:25:01 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
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Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional

Hi Uwe,

On Mon, Jan 17, 2022 at 6:06 PM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
> On Mon, Jan 17, 2022 at 02:08:19PM +0100, Geert Uytterhoeven wrote:
> > On Mon, Jan 17, 2022 at 12:49 PM Uwe Kleine-König
> > <u.kleine-koenig@...gutronix.de> wrote:
> > > > The logic in e.g. drivers/tty/serial/sh-sci.c and
> > > > drivers/spi/spi-rspi.c could be simplified and improved (currently
> > > > it doesn't handle deferred probe) if platform_get_irq_optional()
> > > > would return 0 instead of -ENXIO.

> > > Also for spi-rspi.c I don't see how platform_get_irq_byname_optional()
> > > returning 0 instead of -ENXIO would help. Please talk in patches.

[...]

> This is not a simplification, just looking at the line count and the
> added gotos. That's because it also improves error handling and so the
> effect isn't easily spotted.

Yes, it's larger because it adds currently missing error handling.

> What about the following idea (in pythonic pseudo code for simplicity):

No idea what you gain by throwing in a language that is irrelevant
to kernel programming (why no Rust? ;-)

> > > > So there are three reasons: because the absence of an optional IRQ
> > > > is not an error, and thus that should not cause (a) an error code
> > > > to be returned, and (b) an error message to be printed, and (c)
> > > > because it can simplify the logic in device drivers.
> > >
> > > I don't agree to (a). If the value signaling not-found is -ENXIO or 0
> > > (or -ENODEV) doesn't matter much. I wouldn't deviate from the return
> > > code semantics of platform_get_irq() just for having to check against 0
> > > instead of -ENXIO. Zero is then just another magic value.
> >
> > Zero is a natural magic value (also for pointers).
> > Errors are always negative.
> > Positive values are cookies (or pointers) associated with success.
>
> Yeah, the issue where we don't agree is if "not-found" is special enough
> to deserve the natural magic value. For me -ENXIO is magic enough to
> handle the absence of an irq line. I consider it even the better magic
> value.

It differs from other subsystems (clk, gpio, reset), which do return
zero on not found.
What's the point in having *_optional() APIs if they just return the
same values as the non-optional ones?


Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds