Re: [PATCH] hw/ide: Fix crash when plugging a piix3-ide device into the x-remote machine

[Philippe Mathieu-Daudé]

On 4/27/21 7:16 PM, John Snow wrote:
> On 4/27/21 9:54 AM, Stefan Hajnoczi wrote:
>> I suggest fixing this at the qdev level. Make piix3-ide have a
>> sub-device that inherits from ISA_DEVICE so it can only be instantiated
>> when there's an ISA bus.
>>
>> Stefan
> 
> My qdev knowledge is shaky. Does this imply that you agree with the
> direction of Thomas's patch, or do you just mean to disagree with Phil
> on his preferred course of action?

My understanding is a disagreement to both, with a 3rd direction :)

I agree with Stefan direction but I'm not sure (yet) that a sub-device
is the best (long-term) solution. I guess there is a design issue with
this device, and would like to understanding it first.

IIUC Stefan says the piix3-ide is both a PCI and IDE device, but QOM
only allow a single parent. Multiple QOM inheritance is resolved as
interfaces, but PCI/IDE qdev aren't interfaces, rather abstract objects.
So he suggests to embed an IDE device within the PCI piix3-ide device.

My view is the PIIX is a chipset that share stuffs between components,
and the IDE bus belongs to the chipset PCI root (or eventually the
PCI-ISA bridge, function #0). The IDE function would use the IDE bus
from its root parent as a linked property.
My problem is currently this device is user-creatable as a Frankenstein
single PCI function, out of its chipset. I'm not sure yet this is a
dead end or I could work something out.

Regards,

Phil.