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

[Blue Swirl]

On Mon, May 21, 2012 at 6:28 PM, Peter Maydell <address@hidden> wrote:
> On 21 May 2012 19:08, Blue Swirl <address@hidden> wrote:
>> On Mon, May 21, 2012 at 10:36 AM, Peter Maydell
>> <address@hidden> wrote:
>>> I think it would be nice to have this in upstream qemu; however adding
>>> transaction properties to the IO interface would be quite tricky I
>>> suspect...
>>
>> This is limited to CPU and CPU local bus devices (not generic like
>> PCI), so there could be an out of band mechanism to get/set the
>> additional data.
>
> What's your definition of "generic" here? AMBA isn't particularly
> limited to CPU local bus devices either, really (for instance
> the connection between a versatile express CPU daughterboard
> and the motherboard includes an AMBA AXI bus).

I'd expect that only AMBA devices (ARM specific) would care about the
properties, while for example NE2k could not care less.

>
>> For example store in op_helper.c could use
>> cpu_set_amba_properties(...) before the store and afterwards
>> cpu_get_amba_reply(...).
>
> We really don't want to do two helper function calls for every
> load or store! If you're going to implement them at all then
> you need a more efficient implementation than that...

How about lazy evaluation: generate the properties/evaluate reply only
if the device wants them via
device_get_properties()/device_set_reply(). Then the transaction
overhead could be ignored by everyone if not needed.

>
> -- PMM