Re: [PATCH 11/20] spapr: Fix indexing of XICS irqs

[Greg Kurz]

On Thu, 26 Sep 2019 11:31:48 +1000
David Gibson <address@hidden> wrote:

> On Wed, Sep 25, 2019 at 10:17:46PM +0200, Greg Kurz wrote:
> > On Wed, 25 Sep 2019 16:45:25 +1000
> > David Gibson <address@hidden> wrote:
> > 
> > > spapr global irq numbers are different from the source numbers on the ICS
> > > when using XICS - they're offset by XICS_IRQ_BASE (0x1000).  But
> > > spapr_irq_set_irq_xics() was passing through the global irq number to
> > > the ICS code unmodified.
> > > 
> > > We only got away with this because of a counteracting bug - we were
> > > incorrectly adjusting the qemu_irq we returned for a requested global irq
> > > number.
> > > 
> > > That approach mostly worked but is very confusing, incorrectly relies on
> > > the way the qemu_irq array is allocated, and undermines the intention of
> > > having the global array of qemu_irqs for spapr have a consistent meaning
> > > regardless of irq backend.
> > > 
> > > So, fix both set_irq and qemu_irq indexing.  We rename some parameters at
> > > the same time to make it clear that they are referring to spapr global
> > > irq numbers.
> > > 
> > > Signed-off-by: David Gibson <address@hidden>
> > > ---
> > 
> > Reviewed-by: Greg Kurz <address@hidden>
> > 
> > Further cleanup could be to have the XICS backend to only take global
> > irq numbers and to convert them to ICS source numbers internally. This
> > would put an end to the confusion between srcno/irq in the frontend
> > code.
> 
> Yeah, maybe.  But the local srcnos do actually make sense from within
> the perspective of ICS, so I'm not all that keen to do that.
> 

Not sure to understand what you mean by "within the perspective of ICS".

My concern is actually to get rid of ics->offset users in spapr_irq.c.

eg,

static void spapr_irq_set_irq_xics(void *opaque, int irq, int val)
{
    SpaprMachineState *spapr = opaque;
    uint32_t srcno = irq - spapr->ics->offset;

    ics_set_irq(spapr->ics, srcno, val);
}

It looks like we should do something like:

static void spapr_irq_set_irq_xics(void *opaque, int irq, int val)
{
    SpaprMachineState *spapr = opaque;

    ics_set_irq(spapr->ics, irq, val);
}

and have ics_set_irq() do:

    uint32_t srcno = irq - spapr->ics->offset;

Are you inferring that it is better to keep the irq to srcno conversions
in spapr_irq.c ?

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