[PATCH 2/4] powerpc/mpic: Use the MPIC_LARGE_VECTORS flag for FSL MPIC.

[Sethi Varun-B16395]

> -----Original Message-----
> From: Kumar Gala [mailto:galak at kernel.crashing.org]
> Sent: Tuesday, March 27, 2012 7:01 PM
> To: Sethi Varun-B16395
> Cc: Linuxppc-dev at lists.ozlabs.org
> Subject: Re: [PATCH 2/4] powerpc/mpic: Use the MPIC_LARGE_VECTORS flag
> for FSL MPIC.
> 
> 
> On Mar 27, 2012, at 7:15 AM, Varun Sethi wrote:
> 
> > FSL MPIC supports 16 bit vectors so our vector number space isn't
> > restricted to 256 vectors. We should use the MPIC_LARG_VECTORS flag
> > while intializing the MPIC. This also prevents us from eating in to
> > hardware vector number space (MSIs) while setting up internal sources.
> 
> What is driving this change?  The commit message isn't quite correct as
> MPIC_LARGE_VECTORS is about the # of IRQs, not the fact that vector field
> is 16-bits.
> 
[Sethi Varun-B16395] We derive the internal interrupt source vector numbers from the
number of supported hardware interrupt sources. With the current value of 256
we end up using vector numbers (for internal sources) corresponding to actual hardware
interrupts. With the MPIC_LARGE_VECTORS flag we can avoid eating in to hardware vector
number space.

-Varun