Re: [PATCH] hw: ppc: sam460ex: Disable Ethernet devicetree nodes

[Philippe Mathieu-Daudé]

On 8/16/21 12:26 PM, Peter Maydell wrote:
> On Mon, 16 Aug 2021 at 06:46, David Gibson <david@gibson.dropbear.id.au> 
> wrote:
>>
>> On Sun, Aug 15, 2021 at 07:59:15PM -0700, Guenter Roeck wrote:
>>> IBM EMAC Ethernet controllers are not emulated by qemu. If they are
>>> enabled in devicetree files, they are instantiated in Linux but
>>> obviously won't work. Disable associated devicetree nodes to prevent
>>> unpredictable behavior.
>>>
>>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>>
>> I'll wait for Zoltan's opinion on this, but this sort of thing is why
>> I was always pretty dubious about qemu *loading* a dtb file, rather
>> than generating a dt internally.
> 
> My take is that if you have to modify the dtb file to get QEMU to
> work, then that's a bug in QEMU that should be fixed. It's no
> worse than for the machines we have that don't use dtb and where
> the kernel just knows what the hardware is. (In my experience
> Arm kernels can be a bit finicky about wanting the right dtb
> and not some earlier or later one, so I think at least for Arm
> trying to generate a dt for our non-virt boards would have been
> pretty painful and liable to "new kernels don't boot any more" bugs.)
> 
> Is it sufficient to create stub "unimplemented-device" ethernet
> controllers here, or does the guest want more behaviour than that?

For raspi4 "unimplemented-device" is not enough, so what would
be the ideal resolution for "the guest wants more behaviour"
when we don't have time / interest / specs for the missing
pieces?