Re: [PATCH] hw/intc/arm_gic: Fix set/clear pending of PPI/SPI

[Luc Michel]

Hi Sebastian,

On 11:49 Fri 09 Jul     , Sebastian Huber wrote:
> According to the GICv3 specification register GICD_ISPENDR0 is Banked for each
You're referring to GICv3 but actually modifying GICv2 model. Having a
look at GICv2 reference manual, your affirmation still hold though.

> connected PE with GICR_TYPER.Processor_Number < 8.  For Qemu this is the case
> since GIC_NCPU == 8.
This is GICv3 specific. For GICv2 the architectural limit is 8 CPUs.

> 
> For SPI, make the interrupt pending on all CPUs and not just the processor
> targets of the interrupt.
So you're not referring to GICD_ISPENDR0 anymore right? SPIs starts at
IRQ number 32.  GICD_ISPENDR0 is for IRQs 0 to 31, which are SGIs and
PPIs (This is why this reg is banked, meaning that a CPU can only
trigger a PPI of its own). Maybe make it clear in your commit message
that you are now talking about GICD_ISPENDRn with n > 0

Moreover your statement regarding SPIs seems weird to me. Setting an
SPI pending (in GICD_ISPENDRn with n > 0) should really be like having
it being triggered from the IRQ line. It makes it pending in the
distributor. The distributor then forward it as normal. Why the
GICD_ITARGETSRn configuration should be ignored in this case? At least I
can't find any reference to such a behaviour in the reference manual.

> 
> This behaviour is at least present on the i.MX7D which uses an 
> Cortex-A7MPCore.
Which has a GICv2, not a v3 right?

> 
> Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
> ---
>  hw/intc/arm_gic.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/intc/arm_gic.c b/hw/intc/arm_gic.c
> index a994b1f024..8e377bac59 100644
> --- a/hw/intc/arm_gic.c
> +++ b/hw/intc/arm_gic.c
> @@ -1294,12 +1294,14 @@ static void gic_dist_writeb(void *opaque, hwaddr 
> offset,
>  
>          for (i = 0; i < 8; i++) {
>              if (value & (1 << i)) {
> +                int cm = (irq < GIC_INTERNAL) ? (1 << cpu) : ALL_CPU_MASK;
> +
Indeed, I think the current implementation for PPIs is wrong
(GIC_DIST_TARGET(irq + i) is probably 0 in this case, so a set pending
request for a PPI will get incorrectly ignored). So I agree with the irq <
GIC_INTERNAL case. But for SPIs my concerns still hold (see my comment
in the commit message).

>                  if (s->security_extn && !attrs.secure &&
>                      !GIC_DIST_TEST_GROUP(irq + i, 1 << cpu)) {
>                      continue; /* Ignore Non-secure access of Group0 IRQ */
>                  }
>  
> -                GIC_DIST_SET_PENDING(irq + i, GIC_DIST_TARGET(irq + i));
> +                GIC_DIST_SET_PENDING(irq + i, cm);
>              }
>          }
>      } else if (offset < 0x300) {
> @@ -1317,11 +1319,10 @@ static void gic_dist_writeb(void *opaque, hwaddr 
> offset,
>                  continue; /* Ignore Non-secure access of Group0 IRQ */
>              }
>  
> -            /* ??? This currently clears the pending bit for all CPUs, even
> -               for per-CPU interrupts.  It's unclear whether this is the
> -               corect behavior.  */
>              if (value & (1 << i)) {
> -                GIC_DIST_CLEAR_PENDING(irq + i, ALL_CPU_MASK);
> +                int cm = (irq < GIC_INTERNAL) ? (1 << cpu) : ALL_CPU_MASK;
> +
> +                GIC_DIST_CLEAR_PENDING(irq + i, cm);
I agree with this change too, but you are modifying the GICD_ICPENDRn
register behaviour without mentioning it in the commit message.

Thanks,

-- 
Luc