Re: [Xen-devel] [PATCH] xen/arm: Missing +1 when then number of interrupt lines for the GIC is computed

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-04-25 at 10:52 +0100, Julien Grall wrote:
> On 04/25/2013 09:10 AM, Ian Campbell wrote:
> 
> > On Wed, 2013-04-24 at 20:44 +0100, Julien Grall wrote:
> >> In the GIC manual, the number of interrupt lines is computed with the 
> >> following
> >> formula: 32(N + 1) where N is the value retrieved from GICD_TYPER.
> > 
> > My copy of the manual says "The ITLinesNumber field only indicates the
> > maximum number of SPIs that the GIC might support", which excludes SGIs
> > and PPIs. On the other hand it also says that 0b0011 == 128 interrupts,
> > with ID 0..127, and elsewhere it includes SPI and PPI in the term
> > interrupts.
> > 
> > So it's not really clear, but I think your interpretation is likely
> > correct.
> 
> Perhaps we need to add a comment to describe the "lines" field to avoid
> confusion later.

Yes, please.

> > The impact of getting this count wrong is that currently we don't
> > initialise the final 32 interrupts worth of the GICD_FOOn registers, is
> > that right?
> 
> 
> Right.

If you are respinning please could you mention this in the changelog,
it's the headline feature of the patch really ;-)

Ian.


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