Re: [Qemu-devel] How to generate custom fw paths for IDE devices?

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

On 19/07/18 09:10, Thomas Huth wrote:

> On 18.07.2018 23:13, Mark Cave-Ayland wrote:
>> Hi all,
>>
>> Following on from a couple of patches I've previously posted to the
>> mailing list at
>> https://lists.gnu.org/archive/html/qemu-devel/2018-06/msg08836.html I've
>> made some good progress with trying to add bootindex support to OpenBIOS
>> but I'm stuck with generating the IDE device paths from QEMU.
>>
>> According to OpenBIOS the device path for a cdrom on a sun4u machine
>> should be:
>>
>>    /pci@1fe,0/pci@1,1/ide@3/ide1@8100/cdrom@0
>>
>> whereas with my working patchset I'm currently generating:
>>
>>    /pci@1fe,0/pci@1,1/ide@3/drive@1
>>
>> The issue is that the drive@1 part is being generated by the IDE drive
>> device attached to the IDE bus in hw/ide/qdev.c, and so I think I need
>> to override idebus_get_fw_dev_path() to manually generate the remainder
>> of the path including both the controller and the correctly named drive
>> node.
>>
>> One option may be to consider subclassing IDEBus and overriding
>> idebus_get_fw_dev_path() there, but the cmd646 device is a child of
>> TYPE_PCI_IDE which has its own internal IDEBus and so it seems
>> overriding it is impossible.
>>
>> Can anyone point me in the right direction as to how to generate the
>> correct fw path for IDE devices in the above format for sun4u machines?
> 
> Not sure if it is of any help, but the pseries machine is also rewriting
> the device paths for the device tree: See function spapr_get_fw_dev_path
> in hw/ppc/spapr.c.

Ah I see - this is very useful indeed, as it seemingly allows all the fw 
paths to be managed in a single place without having to add Bus support. 
Thanks for the reference!


ATB,

Mark.