Re: [Qemu-devel] [PATCH v1 2/3] memory: Add sysbus memory device

[Peter Crosthwaite]

On Wed, Apr 16, 2014 at 10:24 PM, Alexander Graf <address@hidden> wrote:
>
> On 15.04.14 04:21, Peter Crosthwaite wrote:
>>
>> Add a sysbus device consisting of a single ram. This allows for
>> instantiation of RAM just like any other device. There are a number
>> of good reasons to want to do this this:
>>
>> 1: Consistency. RAM is not that special where board level files should
>> have to instantiate it with a completely different API. This reduces
>> complexity of board level development by hiding the memory API
>> completely and handling everything via the sysbus API.
>>
>> 2: Device tree completeness. Ram Now shows up in info-qtree and
>> friends. E.g. Info qtree gives meaningful information under the
>> root system bus:
>>
>>    dev: sysbus-memory, id "zynq.ocm_ram"
>>      size = 262144 (0x40000)
>>      read-only = false
>>      irq 0
>>      mmio 00000000fffc0000/0000000000040000
>>    dev: sysbus-memory, id "zynq.ext_ram"
>>      size = 134217728 (0x8000000)
>>      read-only = false
>>      irq 0
>>      mmio 0000000000000000/0000000008000000
>>
>> 3: Remove dependence of global state. Board files don't have to
>> explicity request the global singleton (and much unloved)
>> address_space_memory() and go hacking on it. address_space_memory()
>> is still ultimately used, but the ugliness is hidden in one place - the
>> sysbus core (we can fix that another day).
>>
>> 4: Data driven machine creation. There is list discussion on being able
>> to create or append-to sysbus machines in a data-driven way (whether
>> thats from command-line, monitor or scripts or whatever). This patch
>> removes the memory special case from that problem and allows RAM
>> instantiation to come via whatever solutions we come up with sysbus
>> device instantiation.
>>
>> Signed-off-by: Peter Crosthwaite <address@hidden>
>
>
> Could you please show that this approach works for more complicated
> machines, like x86's pc machine and its PCI holes?
>

Hi Alex,

Do you mean attaching it within a PCI address space? Im not sure
that's valid. That would require some sort of generalisation that
applied to both sysbus and PCI. I actually had a go at something like
this a while back. Basically, the setup was for PCI devices to inherit
from sysbus. This allowed solving the reverse problem. Attaching a PCI
device to sysbus. I guess with a few changes it could be made to work
both ways, but it seems the sysbus and PC world are completely
separate the way the tree stands today.

Regards,
Peter

>
> Alex
>
>