Re: [PATCH 6/7] spi/mpc8xxx: don't check platform_get_irq's returnvalue against zero

From: Uwe Kleine-König
Date: Wed Dec 16 2009 - 12:49:20 EST


[Note the email address used for David Vrabel isn't valid any more,
this mail uses his last used address.]

On Wed, Dec 16, 2009 at 07:32:29PM +0300, Anton Vorontsov wrote:
> On Wed, Dec 16, 2009 at 05:10:08PM +0100, Uwe Kleine-König wrote:
> > platform_get_irq returns -ENXIO on failure, so !irq was probably
> > always true. Better use (int)irq <= 0. Note that a return value of
> > zero is still handled as error even though this could mean irq0.
> >
> > This is a followup to 305b3228f9ff4d59f49e6d34a7034d44ee8ce2f0 that
> > changed the return value of platform_get_irq from 0 to -ENXIO on error.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > ---
> Noooooo... :-(
> Please revert 305b3228f9ff4d59f49e6d34a7034d44ee8ce2f0 instead,
> and fix platforms to remap HWIRQ0 to something that is not VIRQ0.
> IRQ0 is invalid for everything that is outside of arch/*.
First note that my check is safe with both variants (e.g. it does the
right thing independent of the error being signaled by 0 or

Then arch/arm/mach-pxa/devices.c has:

static struct resource pxa27x_resource_ssp3[] = {
[1] = {
.start = IRQ_SSP3,
.end = IRQ_SSP3,

with IRQ_SSP3 being zero (sometimes). The driver is implemented in
arch/arm/mach-pxa/ssp.c and uses platform_get_irq. So according to your
definition it's allowed (arch/* only). Still this would break if you
revert 305b3228f9.

Actually I don't care much, but as platform_get_irq returns an int I
think it's fine for it to signal an error using a value < 0 as irqs are
not negative.

My position regarding irq0 is: If a variable holds either a valid irq
or a value indicating "no irq", then feel free to use 0 as "no irq" and
a value > 0 for a valid irq (without offset). If you want irq0 here,
you're out of luck. But if you have a variable holding a valid irq only
(that is, there is no doubt if the value is valid or not) I see no
reason to dogmatically prohibit irq0.

I'm a bit annoyed as this is the third time[1] this month this irq0
discussion pops up for me. I think people see that irq0 is involved
somehow, start wailing and stop seeing the issues being fixed.

Best regards

[1] one is:
the other wasn't on lkml, only mm-commits. Cannot find it on the
net now.
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | |
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