Re: [Qemu-devel] [PATCH v5 4/8] hw: arm_gic: Keep track of SGI sources

[Christoffer Dall <christoffer.dall@linaro.org>]

On Fri, Jan 31, 2014 at 06:33:25PM +0000, Peter Maydell wrote:
> On 28 January 2014 20:32, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> > Right now the arm gic emulation doesn't keep track of the source of an
> > SGI (which apparently Linux guests don't use, or they're fine with
> > assuming CPU 0 always).
> >
> > Add the necessary matrix on the GICState structure and maintain the data
> > when setting and clearing the pending state of an IRQ and make the state
> > visible to the guest.
> >
> > Note that we always choose to present the source as the lowest-numbered
> > CPU in case multiple cores have signalled the same SGI number to a core
> > on the system.
> 
> > @@ -531,9 +576,29 @@ static void gic_dist_writeb(void *opaque, hwaddr offset,
> >                  GIC_CLEAR_EDGE_TRIGGER(irq + i);
> >              }
> >          }
> > -    } else {
> > +    } else if (offset < 0xf10) {
> >          /* 0xf00 is only handled for 32-bit writes.  */
> >          goto bad_reg;
> > +    } else if (offset < 0xf20) {
> > +        /* GICD_CPENDSGIRn */
> > +        if (s->revision == REV_11MPCORE || s->revision == REV_NVIC) {
> > +            goto bad_reg;
> > +        }
> > +        irq = (offset - 0xf10);
> > +
> > +        GIC_CLEAR_PENDING(irq, 1 << cpu);
> > +        s->sgi_pending[irq][cpu] &= ~value;
> 
> This doesn't look quite right. If the SGI is pending
> from multiple source CPUs and we use CPENDSGIRn to
> clear the bits corresponding to only some of those
> source CPUs, then the interrupt as a whole should stay
> pending on this (target) CPU. I think this is:
> 
>     s->sgi_pending[irq][cpu] &= ~value;
>     if (s->sgi_pending[irq][cpu] == 0) {
>         GIC_CLEAR_PENDING(irq, 1 << cpu);
>     }

I had this vague feeling that it was too easy when I wrote the code,
nice catch!

> 
> (compare the code in gic_acknowledge_irq())
> 
> If you fix that, then
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
> 

Thanks!
-Christoffer