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Re: [Qemu-devel] [PATCH 1/6] s390x/virtio-ccw: enable has_dynamic_sysbus


From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 1/6] s390x/virtio-ccw: enable has_dynamic_sysbus
Date: Wed, 22 Apr 2015 14:21:36 +0200


> Am 22.04.2015 um 13:40 schrieb Cornelia Huck <address@hidden>:
> 
> On Wed, 22 Apr 2015 11:14:40 +0200
> Alexander Graf <address@hidden> wrote:
> 
>>> On 04/22/2015 10:25 AM, Cornelia Huck wrote:
>>> On Tue, 21 Apr 2015 21:06:42 +0200
>>> Alexander Graf <address@hidden> wrote:
>>> 
>>>>> On 04/17/2015 09:52 AM, Cornelia Huck wrote:
>>>>> From: Xu Wang <address@hidden>
>>>>> 
>>>>> We have to enable this flag to support dynamically adding devices to the
>>>>> sysbus. This change is needed for the the upcoming diag288 watchdog.
>>>> s390 doesn't have a "sysbus" per se. Please create a new bus type.
>>> So what's wrong with the sysbus? I don't see why we should be different
>>> than everyone else.
>> 
>> The idea behind sysbus is that you have MMIO, PIO and IRQ pins 
>> connecting to a PIC. It provides a lot of infrastructure for those 
>> interfaces. S390 doesn't use any of them and instead wants registration 
>> on "diag" interfaces for example which I'd put on the same layer as PIO 
>> or MMIO registration.
> 
> I don't think a "diag" bus makes sense.

You don't need a bus necessarily, just a parent class.

> The individual diagnoses are
> way too heterogenous beyond the fact that they use the same base
> instruction.
> 
> So where's the proper place for "misc" devices? My impression was that
> they can go on the sysbus.
> 

If you really don't want to create your own class, how about you inherit from 
the DeviceState class?

Alex


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