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From: Thomas Huth <thuth@redhat.com>
Message-ID: <565E15B6.60501@redhat.com>
Date: Tue, 1 Dec 2015 22:48:38 +0100
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Subject: Re: [Qemu-devel] [PATCH] spapr/pci: populate PCI DT in reverse order
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To: Greg Kurz <gkurz@linux.vnet.ibm.com>, David Gibson <david@gibson.dropbear.id.au>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>

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 /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.

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 <thuth@redhat.com>