Greg Kurz <gr...@kaod.org> writes: > From: Greg Kurz <gk...@linux.vnet.ibm.com> > > Since commit 1d2d974244c6 "spapr_pci: enumerate and add PCI device tree", QEMU > populates the PCI device tree in the opposite order compared to SLOF. > > Before 1d2d974244c6: > > Populating /pci@800000020000000 > 00 0000 (D) : 1af4 1000 virtio [ net ] > 00 0800 (D) : 1af4 1001 virtio [ block ] > 00 1000 (D) : 1af4 1009 virtio [ network ] > Populating /pci@800000020000000/unknown-legacy-device@2 > > 7e5294b8 : /pci@800000020000000 > 7e52b998 : |-- ethernet@0 > 7e52c0c8 : |-- scsi@1 > 7e52c7e8 : +-- unknown-legacy-device@2 ok > > Since 1d2d974244c6: > > Populating /pci@800000020000000 > 00 1000 (D) : 1af4 1009 virtio [ network ] > Populating /pci@800000020000000/unknown-legacy-device@2 > 00 0800 (D) : 1af4 1001 virtio [ block ] > 00 0000 (D) : 1af4 1000 virtio [ net ] > > 7e5e8118 : /pci@800000020000000 > 7e5ea6a0 : |-- unknown-legacy-device@2 > 7e5eadb8 : |-- scsi@1 > 7e5eb4d8 : +-- ethernet@0 ok > > This behaviour change is not actually a bug since no assumptions should be > made on DT ordering. But it has no real justification either, other than > being the consequence of the way fdt_add_subnode() inserts new elements > to the front of the FDT rather than adding them to the tail. > > This patch reverts to the historical SLOF ordering by walking PCI devices > in reverse order. This reconciles pseries with x86 machine types behavior. > It is expected to make things easier when porting existing applications to > power. > > Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com> > Tested-by: Thomas Huth <th...@redhat.com> > Reviewed-by: Nikunj A Dadhania <nik...@linux.vnet.ibm.com> > (slight update to the changelog) > Signed-off-by: Greg Kurz <gr...@kaod.org> > --- > hw/pci/pci.c | 28 ++++++++++++++++++++++++++++ > hw/ppc/spapr_pci.c | 12 ++++++------ > include/hw/pci/pci.h | 4 ++++ > 3 files changed, 38 insertions(+), 6 deletions(-) > > David, > > This patch was posted and already discussed during 2.5 development: > > http://patchwork.ozlabs.org/patch/549925/ > > The "consensus" at the time was that guests should not rely on device > ordering (i.e. use persistent naming instead). > > I got recently contacted by OpenStack people who had several complaints > about the reverse ordering of PCI devices in pseries: different behavior > between ppc64 and x86, lots of time spent in debugging when porting > applications from x86 to ppc64 before realizing that it is caused by the > reverse ordering, necessity to carry hacky workarounds... > > One strong argument against handling this properly with persistent naming > is that it requires systemd/udev. This option is considered as painful > with CirrOS, which aims at remaining as minimal as possible and is widely > used in the OpenStack ecosystem. > > Would you re-consider your position and apply this patch ?
+1 I was the one who introduced the reverse ordering inadvertently. Regards Nikunj
