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

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Date:	Tue, 3 Mar 2009 11:39:43 -0600
From:	Dimitri Sivanich <sivanich@....com>
To:	Ingo Molnar <mingo@...e.hu>
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

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?

> 
> > +#ifdef CONFIG_X86_64
> > +extern void generic_interrupt(void);
> > +#endif
> 
> in any case please make it symmetric across 32-bit and 64-bit - 
> even though UV is 64-bit only.

OK.

> 
> 	Ingo
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