xen/arm: Allow DOM0 to set the IRQ type

xen/arm: Allow DOM0 to set the IRQ type

The function route_irq_to_guest mandates the IRQ type, stored in
desc->arch.type, to be valid. However, in case of ACPI, these
information is not part of the static tables. Therefore Xen needs to
rely on DOM0 to provide a valid type based on the firmware tables.

A new helper, irq_type_set_by_domain is provided to check whether a
domain is allowed to set the IRQ type. For now, only DOM0 is allowed to
configure.

When the helper returns 1, the routing function will not check whether
the IRQ type is correctly set and configure the GIC. Instead, this will
be done when the domain will enable the interrupt.

Note that irq_set_spi_type is not called because it validates the type
and does not allow it the domain to change the type after the first
write. It means that desc->arch.type may never be set, which is fine
because the field is only used to configure the type during the routing.

Based on 4.3.13 in ARM IHI 0048B.b, changing the value of Int_config is
UNPREDICTABLE when the corresponding interrupt is not disabled.

Therefore, setting the IRQ type when the guest is writing into ICFGR
would require more work to make sure the IRQ has been disabled before
writing into the host ICFGR. As the behavior is UNPREDICTABLE, the type
will be set before enabling the physical IRQ associated to the virtual IRQ.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>