q35: change defaults for kernel irqchip and IR

v2:
- drop patch 1, so we don't even need to consider old kernels for the default value [Paolo, Eduardo]
- fix up commit message of the split irqchip patch to mention that

============= Original cover letter ================

This only changes q35. Nothing else.

Before this series, we have these default parameters:

- machine kernel-irqchip: on
- intel-iommu IR: off

This series wants to change these default variables into:

- machine kernel-irqchip: split
- intel-iommu IR: on

and at the meantime we should keep compatibility with old kernels and old versions of QEMU.

For old versions of QEMU: we used machine compat properties.

For old kernels (<4.4): if user didn't specify split kernel irqchip, we'll take it only as the first priority if it's supported by the kernel; otherwise, we will continue with complete kernel irqchip.

Both of these parameters should be good to have (split irqchip gains more security, while IR gets it too but even more, like x2apic). So let's try to make them as default if capable.

Tests ("split" stands for whether kernel split irqchip enabled, "IR" stands for whether IR is turned on):

   |--------------------------------------------------------+-------+----|
   | params                                                 | split | IR |
   |--------------------------------------------------------+-------+----|
   | -M q35                                                 |     0 | /  |
   | -M q35,accel=kvm                                       |     1 | /  |
   | -M pc-q35-3.1,accel=kvm                                |     0 | /  |
   | -M q35,accel=kvm,kernel-irqchip=off                    |     0 | /  |
   | -M q35,accel=kvm,kernel-irqchip=on                     |     0 | /  |
   | -M q35 -device intel-iommu                             |     0 | 1  |
   | -M q35,accel=kvm -device intel-iommu                   |     1 | 1  |
   | -M q35,accel=kvm,kernel-irqchip=on -device intel-iommu |     0 | 0  |
   |--------------------------------------------------------+-------+----|

I didn't try old kernels, though.

Any comment would be welcomed, thanks.

Peter Xu (3):
q35: set split kernel irqchip as default
x86-iommu: switch intr_supported to OnOffAuto type
x86-iommu: turn on IR by default if proper

 hw/core/machine.c           |  2 ++
 hw/i386/acpi-build.c        |  6 +++---
 hw/i386/amd_iommu.c         |  2 +-
 hw/i386/intel_iommu.c       |  6 +++---
 hw/i386/pc.c                |  2 +-
 hw/i386/pc_q35.c            |  2 ++
 hw/i386/x86-iommu.c         | 18 +++++++++++++++---
 include/hw/boards.h         |  1 +
 include/hw/i386/x86-iommu.h |  4 +++-
 9 files changed, 31 insertions(+), 12 deletions(-)

2.17.1