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Re: [Qemu-ppc] [PATCH] spapr/pci: populate PCI DT in reverse order
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From: |
Greg Kurz |
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Subject: |
Re: [Qemu-ppc] [PATCH] spapr/pci: populate PCI DT in reverse order |
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Date: |
Mon, 27 Feb 2017 23:20:16 +0100 |
David,
Any chances to have this in 2.9 ?
On Wed, 22 Feb 2017 11:56:53 +0100
Greg Kurz <address@hidden> wrote:
> From: Greg Kurz <address@hidden>
>
> 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 /address@hidden
> 00 0000 (D) : 1af4 1000 virtio [ net ]
> 00 0800 (D) : 1af4 1001 virtio [ block ]
> 00 1000 (D) : 1af4 1009 virtio [ network ]
> Populating /address@hidden/address@hidden
>
> 7e5294b8 : /address@hidden
> 7e52b998 : |-- address@hidden
> 7e52c0c8 : |-- address@hidden
> 7e52c7e8 : +-- address@hidden ok
>
> Since 1d2d974244c6:
>
> Populating /address@hidden
> 00 1000 (D) : 1af4 1009 virtio [ network ]
> Populating /address@hidden/address@hidden
> 00 0800 (D) : 1af4 1001 virtio [ block ]
> 00 0000 (D) : 1af4 1000 virtio [ net ]
>
> 7e5e8118 : /address@hidden
> 7e5ea6a0 : |-- address@hidden
> 7e5eadb8 : |-- address@hidden
> 7e5eb4d8 : +-- address@hidden 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 <address@hidden>
> Tested-by: Thomas Huth <address@hidden>
> Reviewed-by: Nikunj A Dadhania <address@hidden>
> (slight update to the changelog)
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> 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 ?
>
> Cheers.
>
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index a563555e7da7..273f1e46025a 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -1530,6 +1530,34 @@ static const pci_class_desc pci_class_descriptions[] =
> { 0, NULL}
> };
>
> +static void pci_for_each_device_under_bus_reverse(PCIBus *bus,
> + void (*fn)(PCIBus *b,
> + PCIDevice *d,
> + void *opaque),
> + void *opaque)
> +{
> + PCIDevice *d;
> + int devfn;
> +
> + for (devfn = 0; devfn < ARRAY_SIZE(bus->devices); devfn++) {
> + d = bus->devices[ARRAY_SIZE(bus->devices) - 1 - devfn];
> + if (d) {
> + fn(bus, d, opaque);
> + }
> + }
> +}
> +
> +void pci_for_each_device_reverse(PCIBus *bus, int bus_num,
> + void (*fn)(PCIBus *b, PCIDevice *d, void *opaque),
> + void *opaque)
> +{
> + bus = pci_find_bus_nr(bus, bus_num);
> +
> + if (bus) {
> + pci_for_each_device_under_bus_reverse(bus, fn, opaque);
> + }
> +}
> +
> static void pci_for_each_device_under_bus(PCIBus *bus,
> void (*fn)(PCIBus *b, PCIDevice *d,
> void *opaque),
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index fd6fc1d95344..2a20c2a140fc 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -1782,9 +1782,9 @@ static void spapr_populate_pci_devices_dt(PCIBus *bus,
> PCIDevice *pdev,
> s_fdt.fdt = p->fdt;
> s_fdt.node_off = offset;
> s_fdt.sphb = p->sphb;
> - pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
> - spapr_populate_pci_devices_dt,
> - &s_fdt);
> + pci_for_each_device_reverse(sec_bus, pci_bus_num(sec_bus),
> + spapr_populate_pci_devices_dt,
> + &s_fdt);
> }
>
> static void spapr_phb_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
> @@ -1953,9 +1953,9 @@ int spapr_populate_pci_dt(sPAPRPHBState *phb,
> s_fdt.fdt = fdt;
> s_fdt.node_off = bus_off;
> s_fdt.sphb = phb;
> - pci_for_each_device(bus, pci_bus_num(bus),
> - spapr_populate_pci_devices_dt,
> - &s_fdt);
> + pci_for_each_device_reverse(bus, pci_bus_num(bus),
> + spapr_populate_pci_devices_dt,
> + &s_fdt);
>
> ret = spapr_drc_populate_dt(fdt, bus_off, OBJECT(phb),
> SPAPR_DR_CONNECTOR_TYPE_PCI);
> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> index 6983f13745a5..9349acbfb278 100644
> --- a/include/hw/pci/pci.h
> +++ b/include/hw/pci/pci.h
> @@ -429,6 +429,10 @@ int pci_bus_numa_node(PCIBus *bus);
> void pci_for_each_device(PCIBus *bus, int bus_num,
> void (*fn)(PCIBus *bus, PCIDevice *d, void *opaque),
> void *opaque);
> +void pci_for_each_device_reverse(PCIBus *bus, int bus_num,
> + void (*fn)(PCIBus *bus, PCIDevice *d,
> + void *opaque),
> + void *opaque);
> void pci_for_each_bus_depth_first(PCIBus *bus,
> void *(*begin)(PCIBus *bus, void
> *parent_state),
> void (*end)(PCIBus *bus, void *state),
>
>
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