Re: [Qemu-devel] [PATCH 4/5] configs: Add a CONFIG_UNIMP switch for the "unimplemented-device"

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/10/2018 18:54, Peter Maydell wrote:
> On 19 October 2018 at 17:44, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> On 19/10/2018 18:25, Philippe Mathieu-Daudé wrote:
>>>
>>> First because I'm using it heavily on MIPS and PPC boards, when no
>>> datashits are available.
>>> I'll submit that during the next merge window, although the MIPS tree
>>> seems now reluctant to that kind of hobbyist work.
>>>
>>> Second, because it is very clean when you implement a SoC to first
>>> start with an empty UNIMP region and a cpu core,
>>> then declare the mmio regions for each device (still UNIMP), then you
>>> can slowly add devices one at a time.
>>> This let you (me, so far) push at most a dozen of tiny patches in a
>>> working series, instead of a small series of a dozen of huge patches,
>>> or a series of 100 tiny patches.
>>
>> I don't see however why it's a problem to add/remove CONFIG_UNIMP to
>> default-configs though (in the Kconfig world the board would "select
>> UNIMP").
> 
> Well, it's extra friction for people writing new board models,
> and the benefit of having CONFIG_UNIMP is all to downstream
> redistributors, not to upstream...
> 
> I'm not vetoing this patchset, but I do think that if RedHat
> wants to distribute significantly-cut-down binaries then
> it would be worth working on a mechanism for making that
> more conveniently doable, rather than just hacking up
> the very creaky default-configs/ stuff.

Yes, we are going to meet the NEMU guys at KVM Forum and talk about the
"mini-Kconfig" stuff; in the meanwhile, default-configs/ is what we
have, it was enough while we were caring basically only about x86 and
thus we only needed to disable PCI devices, but now it's showing its age.

Paolo