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Re: [Qemu-ppc] [PATCH 2/2] m48t59: add mem_base value to m48t59_init_isa

From: Andreas Färber
Subject: Re: [Qemu-ppc] [PATCH 2/2] m48t59: add mem_base value to m48t59_init_isa()
Date: Mon, 19 Jan 2015 21:03:40 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0

Am 19.01.2015 um 16:22 schrieb Artyom Tarasenko:
> On Mon, Jan 19, 2015 at 4:01 PM, Andreas Färber <address@hidden> wrote:
>> Am 19.01.2015 um 13:57 schrieb Artyom Tarasenko:
>>> On Mon, Jan 19, 2015 at 1:45 PM, Paolo Bonzini <address@hidden> wrote:
>>>> On 19/01/2015 12:35, Mark Cave-Ayland wrote:
>>>>> Similar to m48t59_init(), add a mem_base value so that NVRAM can be 
>>>>> mapped via
>>>>> MMIO rather than ioport if required.
>>>>> Signed-off-by: Mark Cave-Ayland <address@hidden>
>>>>> ---
>>>> Is it really ISA if it's MMIO?  In other words, why can't this be a
>>>> sysbus device?
>>> On physical machines it's EBus, which is pretty much like 8-bit ISA.
>>> So, I think modelling it as ISA is closer to to the reality.
>>> But out of curiosity, would it be possible to have a sysbus device
>>> somewhere in a middle of PCI space? [...]
>> Why would you want to use a SysBusDevice in the first place?
> Ask Paolo. :-) For me it's only important to have a MMIO device in the
> proper address range.
>> I previously discussed with Mark that it should be an EBusDevice, not an
>> ISADevice or SysBusDevice.
> Interesting. I can't find this discussion in the list archive.

Hm, am I mixing that up with SBus then? There were some helper functions
related to ROM loading being added as context to my suggestion that I
thought could become class fields.

> Do you suggest to
> create EBusDevices for all ISA devices (serial, parallel, keyboard,
> floppy) used in sun4u, or only for m48t59?
> What would be the advantage of using EBusDevice over ISADevice?

For all devices that are in fact EBus devices. The general idea is
encapsulation and abstraction - hiding the implementation detail of
whether it is internally an ISADevice or something else. Such a patch
should be quite trivial. Similarly it gives helper functions and
potential class methods a natural place to live.


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