Re: [Qemu-devel] Morph cpu_reset -> device_reset

[Andreas Färber]

Am 15.07.2013 12:45, schrieb Peter Crosthwaite:
> Hi Andreas,
> 
> On Mon, Jul 15, 2013 at 7:55 PM, Andreas Färber <address@hidden> wrote:
>> Hi Peter,
>>
>> Am 15.07.2013 06:02, schrieb Peter Crosthwaite:
>>> A while ago, TYPE_CPU was refactored to by a child of TYPE_DEVICE. As
>>> something of a hangover though, CPU has a separate reset fn to device.
>>> This means
>>>
>>> device_reset(DEVICE(my_cpu));
>>>
>>> doesn't actually work as a reset. Should we fix this by getting rif of
>>> cpu_reset and just using the device reset API for cpu reset?
>>
>> This question has come up a number of times, cf. the archives. For one,
>> CPU reset is a mess with most CPUs not registering reset handlers of
>> their own like devices do but having machines do that and piggy-back
>> some machine-specific initialization, possibly even relying on execution
>> order of reset handlers.
> 
> So some architectures are going to be a lot easier than others and if
> this is considered the right thing to do, we can convert some of easy
> ones and scratch our heads later re the machine quirks. I can speak
> for Microblaze as being as easy one. ARM doesn't look that scary
> either - and thats the one I want to convert for my application.

See hw/arm/boot.c for where such piggy-backing happens in ARM.

>> For another, some forms of Soft Reset (e.g.,
>> kdump on s390x) will require to reset devices only but not CPUs -
>> currently qdev_devices_reset() calls all reset handlers, not just
>> devices as the name might imply.
>>
>> For now you can reset a CPU via
>>
>> cpu_reset(CPU(my_cpu));
>>
> 
> So my application is clock controllers, which have a uniform reset
> mechanism. I want to avoid having to give my clock controller CPU
> awareness for the sake of being able to do a reset. Infact, I dont
> event want my controller know what its resetting, all it gets is a
> link to a TYPE_DEVICE which it can then reset. Not possible with CPUs
> unless you:
> 
> if (object_dynamic_cast(my_dev, TYPE_CPU))
>    cpu_reset(...);
> else
>    device_reset(...);

Sounds what you are looking for is rather a qemu_irq pin, which Anthony
has been promoting for soft resets, too.

Note that if we made device_reset() work on a CPU then we would need to
place that type check elsewhere still.

Andreas

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