[Qemu-devel] [RFC for-3.2 PATCH 6/7] pcie: Allow generic PCIe root port to specify link speed and width

[Alex Williamson <alex.williamson@redhat.com>]

Allow users to specify speed and width values for the generic PCIe
root port.  Defaults remain at 2.5GT/s & x1 for compatiblity.  Machine
based defaults to increase this, such as if we wanted a pc-q35-3.2
machine to default to 16GT/s & x32, can be triggered by implementing
an instance_init callback here.

Note for libvirt testing that pcie-root-port controllers are given
default names like "pci.7" which don't play well with using the
"-set device.$name.$prop=$value" options accessible to us via
<qemu:commandline> options.  The solution is to add an <alias> to the
pcie-root-port <controller>, for example:

    <controller type='pci' index='7' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='7' port='0x15'/>
      <alias name='ua-gfx0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x5'/>
    </controller>

The "ua-" here is a mandatory prefix.  We can then use:

  <qemu:commandline>
    <qemu:arg value='-set'/>
    <qemu:arg value='device.ua-gfx0.speed=8'/>
    <qemu:arg value='-set'/>
    <qemu:arg value='device.ua-gfx0.width=16'/>
    <qemu:arg value='-set'/>
  </qemu:commandline>

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 hw/pci-bridge/gen_pcie_root_port.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/pci-bridge/gen_pcie_root_port.c b/hw/pci-bridge/gen_pcie_root_port.c
index 299de429ec1e..e3bba2ab68ef 100644
--- a/hw/pci-bridge/gen_pcie_root_port.c
+++ b/hw/pci-bridge/gen_pcie_root_port.c
@@ -124,6 +124,8 @@ static Property gen_rp_props[] = {
                      res_reserve.mem_pref_32, -1),
     DEFINE_PROP_SIZE("pref64-reserve", GenPCIERootPort,
                      res_reserve.mem_pref_64, -1),
+    DEFINE_PROP_PCIE_LINK_SPEED("speed", PCIESlot, speed, PCIE_LINK_SPEED_2_5),
+    DEFINE_PROP_PCIE_LINK_WIDTH("width", PCIESlot, width, PCIE_LINK_WIDTH_1),
     DEFINE_PROP_END_OF_LIST()
 };