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

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Message-ID: <Yd7JTvfblG0Ge4AN@smile.fi.intel.com>
Date:   Wed, 12 Jan 2022 14:27:58 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Uwe Kleine-König 
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Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional

On Wed, Jan 12, 2022 at 11:27:02AM +0100, Geert Uytterhoeven wrote:
> On Wed, Jan 12, 2022 at 9:51 AM Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> wrote:
> > On Wed, Jan 12, 2022 at 09:33:48AM +0100, Geert Uytterhoeven wrote:
> > > On Mon, Jan 10, 2022 at 10:20 PM Andrew Lunn <andrew@...n.ch> wrote:
> > > > On Mon, Jan 10, 2022 at 09:10:14PM +0100, Uwe Kleine-König wrote:
> > > > > On Mon, Jan 10, 2022 at 10:54:48PM +0300, Sergey Shtylyov wrote:
> > > > > > This patch is based on the former Andy Shevchenko's patch:
> > > > > >
> > > > > > https://lore.kernel.org/lkml/20210331144526.19439-1-andriy.shevchenko@linux.intel.com/
> > > > > >
> > > > > > Currently platform_get_irq_optional() returns an error code even if IRQ
> > > > > > resource simply has not been found. It prevents the callers from being
> > > > > > error code agnostic in their error handling:
> > > > > >
> > > > > >     ret = platform_get_irq_optional(...);
> > > > > >     if (ret < 0 && ret != -ENXIO)
> > > > > >             return ret; // respect deferred probe
> > > > > >     if (ret > 0)
> > > > > >             ...we get an IRQ...
> > > > > >
> > > > > > All other *_optional() APIs seem to return 0 or NULL in case an optional
> > > > > > resource is not available. Let's follow this good example, so that the
> > > > > > callers would look like:
> > > > > >
> > > > > >     ret = platform_get_irq_optional(...);
> > > > > >     if (ret < 0)
> > > > > >             return ret;
> > > > > >     if (ret > 0)
> > > > > >             ...we get an IRQ...
> > > > >
> > > > > The difference to gpiod_get_optional (and most other *_optional) is that
> > > > > you can use the NULL value as if it were a valid GPIO.
> > > > >
> > > > > As this isn't given with for irqs, I don't think changing the return
> > > > > value has much sense.
> > > >
> > > > We actually want platform_get_irq_optional() to look different to all
> > > > the other _optional() methods because it is not equivalent. If it
> > > > looks the same, developers will assume it is the same, and get
> > > > themselves into trouble.
> > >
> > > Developers already assume it is the same, and thus forget they have
> > > to check against -ENXIO instead of zero.
> >
> > Is this an ack for renaming platform_get_irq_optional() to
> > platform_get_irq_silent()?
> 
> No it isn't ;-)
> 
> 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.

For the record, I'm on the same page with Geert.

-- 
With Best Regards,
Andy Shevchenko