Re: [Qemu-devel] Get current env within io_handler ?

[Andreas Färber]

Am 21.05.2012 09:21, schrieb nicolas.sauzede:
> Hi Peter, 
> 
>> Message du 19/05/12 11:39
>> De : "Peter Maydell" 
>> A : "Blue Swirl" 
>> Copie à : "nicolas.sauzede" , address@hidden
>> Objet : Re: [Qemu-devel] Get current env within io_handler ?
>>
>> On 19 May 2012 08:13, Blue Swirl wrote:
>>> nicolas.sauzede wrote:
>>>> Well, for example, we have the issue where we need to know if
>>>> the cpu that performs a hardware io is in priviledged/secure mode,
>>>> because some HW devices implemented in TLM requires such special
>>>> flags on certain register accesses.
>>
>>> How does real HW do it? I don't think there is a bus that indicates
>>> the CPU number to the device.
>>
>> The AMBA AXI bus includes attributes for:
>> * secure/nonsecure world (used for TrustZone)
>> * privileged/nonprivileged
>> * instruction/data access
>> * a transaction ID
>>
>> The transaction ID typically encodes "which core in the
>> CPU made this memory transaction?". It's not always
>> meaningful, eg when caching intervenes, but for device
>> access you can use it. I'd tend to expect to see that in
>> testbench setups rather than the real world, though. Looking
>> straightforwardly at the protection attributes as Nicolas
>> suggests is much more standard.
> 
> Ok, so I guess that for now, we have to live with the lack of a way to 
> actually
> get those io transaction properties, right ?
> Do you think it would be feasible to allow it the future ? (for now, I've done
> some shortcuts and ugly hardcoding in my TLM prototype to make things work, 
> but still..)
[...]
> Do you think this feature could be useful/legitimate in upstream qemu ?

You might want to coordinate that with Edgar, he did a TLM integration
once. But I have no clue how close to master his fork is.

Andreas

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