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

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Message-ID: <20220110214448.rp4pcjlaqbjlggvj@pengutronix.de>
Date:   Mon, 10 Jan 2022 22:44:48 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Ulf Hansson <ulf.hansson@...aro.org>,
        Vignesh Raghavendra <vigneshr@...com>, kvm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-iio@...r.kernel.org,
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Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional

On Mon, Jan 10, 2022 at 11:07:03PM +0200, Andy Shevchenko 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.
> 
> The problem is not only there, but also in the platform_get_irq() and that
> problem is called vIRQ0. Or as Linus put it "_cookie_" for IRQ, which never
> ever should be 0.

IMHO it's best to avoid yielding zero for a value that should be
interpreted as an (virtual) irq. Then callers don't even have to
consider if it's a valid value or not.

> > As this isn't given with for irqs, I don't think changing the return
> > value has much sense. In my eyes the problem with platform_get_irq() and
> > platform_get_irq_optional() is that someone considered it was a good
> > idea that a global function emits an error message. The problem is,
> > that's only true most of the time. (Sometimes the caller can handle an
> > error (here: the absence of an irq) just fine, sometimes the generic
> > error message just isn't as good as a message by the caller could be.
> > (here: The caller could emit "TX irq not found" which is a much nicer
> > message than "IRQ index 5 not found".)
> > 
> > My suggestion would be to keep the return value of
> > platform_get_irq_optional() as is, but rename it to
> > platform_get_irq_silent() to get rid of the expectation invoked by the
> > naming similarity that motivated you to change
> > platform_get_irq_optional().
> 
> This won't fix the issue with vIRQ0.

Is the patch about vIRQ0, or did you only start to consider it when I
said that for gpio NULL is a dummy value? If the former, the commit log
should better mention that.

Anyhow, I still think renaming platform_get_irq_optional() to
platform_get_irq_silent() is a good idea and the patches in this thread
are not.

Best regards
Uwe

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

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