[RFC PATCH 3/9] irqchip: GIC: Convert to EOImode == 1

On Wed, Jun 25, 2014 at 4:28 AM, Marc Zyngier [off-list ref] wrote:

So far, GICv2 has been used in with EOImode == 0. The effect of this
mode is to perform the priority drop and the deactivation of the
interrupt at the same time.

While this works perfectly for Linux (we only have a single priority),
it causes issues when an interrupt is forwarded to a guest, and when
we want the guest to perform the EOI itself.

For this case, the GIC architecture provides EOImode == 1, where:
- A write to the EOI register drops the priority of the interrupt and leaves
it active. Other interrupts at the same priority level can now be taken,
but the active interrupt cannot be taken again
- A write to the DIR marks the interrupt as inactive, meaning it can
now be taken again.

We only enable this feature when booted in HYP mode. Also, as most device
trees are broken (they report the CPU interface size to be 4kB, while
the GICv2 CPU interface size is 8kB), output a warning if we're booted
in HYP mode, and disable the feature.

Why not fix-up the size so the feature can be enabled?

Rob