Re: [Xen-devel] [PATCH v5 08/10] xen/arm: second irq injection while the first irq is still inflight

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-03-24 at 18:49 +0000, Stefano Stabellini wrote:
> Set GICH_LR_PENDING in the corresponding GICH_LR to inject a second irq
> while the first one is still active.
> If the first irq is already pending (not active), just clear
> GIC_IRQ_GUEST_PENDING because the irq has already been injected and is
> already visible by the guest.

I'm confused by this.

If the interrupt is pending but not active then the guest has yet to
read GICC_IAR, so while it might be "visible" to the guest it has not
been observed by the guest.

The comment says:

     * GIC_IRQ_GUEST_PENDING: the irq is asserted

I'm not sure how a second irq arriving would correspond to deasserting
the IRQ.

Also if you are clearing GIC_IRQ_GUEST_PENDING without clearing the
pending bit in the LR that's rather confusing -- I thought the state was
supposed to correspond to (the most recently observed) LR state.

(having been told that there should be a v6 I'm going to stop here while
I figure out where it went...)

Ian.


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