Re: [Qemu-ppc] [PATCH] spapr/pci: populate PCI DT in reverse order

[Nikunj A Dadhania]

David Gibson <address@hidden> writes:

> On Thu, Dec 17, 2015 at 09:43:29AM +0100, Greg Kurz wrote:
>> On Thu, 3 Dec 2015 15:53:17 +0100
>> Greg Kurz <address@hidden> wrote:
>> 
>> > On Tue, 1 Dec 2015 22:48:38 +0100
>> > Thomas Huth <address@hidden> wrote:
>> > 
>> > > On 30/11/15 11:45, Greg Kurz wrote:
>> > > > 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.
>> > > 
>> > > I've applied your patch here locally, and indeed, the device tree looks
>> > > nicer to me, too, when the nodes are listed in ascending order.
>> > > 
>> > > Tested-by: Thomas Huth <address@hidden>
>> > > 
>> > > 
>> > 
>> 
>> Ping ?
>
> Sorry I didn't reply.
>
> I'm still dubious about this.  It seems like a fair bit of effort to
> restore a behaviour that the client isn't supposed to be relying on
> anyway.
>
> Plus, the version with the changed order is already released, so
> applying this will mean a second behaviour change.

The behaviour change was not intentional by me, so I would vote for
restoring the old order.

Reviewed-by: Nikunj A Dadhania <address@hidden>

Regards
Nikunj