linux-kernel - Re: [PATCH 1/6 v6] SGI RTC: add generic system interrupt

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Date:	Tue, 3 Mar 2009 19:52:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Dimitri Sivanich <sivanich@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	john stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6 v6] SGI RTC: add generic system interrupt


* Dimitri Sivanich <sivanich@....com> wrote:

> On Tue, Mar 03, 2009 at 04:34:33PM +0100, Ingo Molnar wrote:
> > 
> > * Dimitri Sivanich <sivanich@....com> wrote:
> > 
> > > This patch allocates a system interrupt vector for various 
> > > platform specific uses.
> > 
> > this is really ugly.
> > 
> > Also, why are all these symbols exported? There's no need to 
> > build the UV RTC driver as a module. It's either built-in or not 
> > built-in - it's small enough.
> 
> OK.
> 
> > 
> > this stuff:
> > 
> > > +/* Function pointer for generic interrupt vector handling */
> > > +static void (*generic_interrupt_extension)(void);
> > > +static char generic_show_string[28];
> > > +static char generic_show_prefix[6];
> > > +
> > > +int is_generic_interrupt_registered()
> > > +{
> > > +	if (generic_interrupt_extension)
> > > +		return 1;
> > > +	else
> > > +		return 0;
> > > +}
> > > +
> > > +char *generic_interrupt_string(void)
> > > +{
> > > +	return generic_show_string;
> > > +}
> > > +
> > > +char *generic_interrupt_prefix(void)
> > > +{
> > > +	return generic_show_prefix;
> > > +}
> > 
> > is SMP unsafe, etc. etc. - not something we should ever call 
> > from a module. We just shouldnt do it in this form. What 
> > necessiates it?
> 
> I wanted a way to show specific strings when displaying irq statistics.  We could show these in a more generic way I suppose.
> 
> Any given platform should just be changing these once, hence the lack of need for locking.
> 
> > 
> > All we need is:
> > 
> > > +	/* generic IPI for platform specific use */
> > > +	alloc_intr_gate(GENERIC_INTERRUPT_VECTOR, generic_interrupt);
> > 
> > plus one trivial callback function - and then the UV platform 
> > uses it for its own purpose. It's not like two platforms will be 
> > running at once so there's no locking needed, etc.
> 
> Right.  But still register the callback function as I have it 
> now?

i'd suggest to just override that global function pointer from 
the UV detection routines.

this way we have it in a minimalistically generic fashion, but 
with a minimum amount of fuss around it.

	Ingo
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