Re: [Qemu-devel] [PATCH 0/2 v3] target-i386: refactor reset handling and move it into cpu.c

[Anthony Liguori <aliguori@us.ibm.com>]

Andreas Färber <afaerber@suse.de> writes:

> Am 01.08.2012 22:02, schrieb Anthony Liguori:
>> Devices do one of two things today:
>> 
>> 1) register a reset callback
>> 
>> 2) implement a reset method that is invoked through it's parent bus
>> 
>> Since I don't expect CPUs to exist on a bus, it's not immediately clear
>> to me that (1) isn't going to be what we do for quite some time.
>
> Err, I thought devices implement a function assigned to a
> DeviceClass::reset, no? That would be (2) on your list and we've been
> working on ripping out (1) for devices, on sPAPR for instance.
> (2) is what we already have with CPUClass::reset.

Something has to call DeviceClass::reset.  That's done through a
BusState.  Whenever a bus is created, a qemu_register_reset() call is
made to invoke the reset method on any device that's part of the bus.

So just implementing DeviceClass::reset doesn't automatically mean the
reset function will be called.  In the short term, I think we'll need to
still register a reset handler.

> The only remaining issue is that the CPUClass::reset callback is not
> automatically called on machine/bus reset yet.
>
> And what I was saying is that moving the code is NOT an improvement. It
> is NO functional change and it is NOT a prerequisite for any change on
> the list today. So it is not needed for the to be released 1.2.
>
> A very low hanging fruit for 1.2 would be to register a SINGLE central
> reset callback that iterates through the globally available CPU list and
> calls ->reset on each! Then we can drop the reset callbacks in most
> machines rather than moving old code around.

Relying on the CPU list for this isn't very QOM-like.  A better approach
would be to make all CPUs appear in a container and then have the reset
propagate through container.

Reset is a complicated beast.  While we model a single reset line today,
this isn't technically correct.  I believe the distinction between reset
types start to matter with PCI-e actually.

I do think any reduction in what's happening in machine is a net win.
Even if we refactor this later, having the machine code do less and
devices do more is an improvement.

Regards,

Anthony Liguori

>
> Regards,
> Andreas
>
>> 
>> Regards,
>> 
>> Anthony Liguori
>> 
>>>
>>> Regards,
>>> Andreas
>>>
>>> -- 
>>> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
>>> GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
>> 
>
>
> -- 
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
> GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg