linux-kernel - Re: [PATCH 6/7] spi/mpc8xxx: don't check platform_get

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Date:	Wed, 16 Dec 2009 21:20:34 +0300
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org, David Vrabel <david.vrabel@....com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	Kumar Gala <galak@...nel.crashing.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	spi-devel-general@...ts.sourceforge.net,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 6/7] spi/mpc8xxx: don't check platform_get_irq's return
 value against zero

On Wed, Dec 16, 2009 at 06:49:04PM +0100, Uwe Kleine-König wrote:
[...]
> > 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/*.
> > 
> > http://lkml.org/lkml/2005/11/22/159
> > http://lkml.org/lkml/2005/11/22/213
> > http://lkml.org/lkml/2005/11/22/227
> 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
> -ESOMETHING.)
> 
> Then arch/arm/mach-pxa/devices.c has:
> 
> static struct resource pxa27x_resource_ssp3[] = {
> 	...
> 	[1] = {
> 		.start  = IRQ_SSP3,
> 		.end    = IRQ_SSP3,
> 		.flags  = IORESOURCE_IRQ,
> 	},
> 	...
> }
> 
> with IRQ_SSP3 being zero (sometimes).  The driver is implemented in
> arch/arm/mach-pxa/ssp.c and uses platform_get_irq.

So fix this *one* driver? Implement arm-specific platform_get_irq() as
a band-aid. Or better, implement virtual irqs <-> hardware irqs mapping
for ARM.

[...]
> 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.

For this particular driver, there is NO issue whatsoever. It is
only used for PowerPC, which has VIRQ0 == invalid IRQ. And note
that there still could be HWIRQ0 on PowerPC, but it is *never*
mapped to VIRQ0.

[...]
> [1] one is:
> 	http://thread.gmane.org/gmane.linux.kernel/924739

No wonder the discussion popped up. You're adding some ugly
#ifdef stuff that adds some arch-specific knowledge to a generic
code.

Sure, there's a lot of ugly code even in the kernel/ directly, but
you have to prepare for resistance when you add more of it.

So, if you want to fix the root cause of the issue: revert the
305b3228f9ff4d59f49e6d34a7034d44ee8ce2f0, and try to improve the
ARM land, do not band-aid the whole kernel all over the place.

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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