Re: [Qemu-devel] [PATCH] qdev: Reset hotplugged devices

[Anthony Liguori]

On 08/24/2010 10:07 PM, Isaku Yamahata wrote:
> On Fri, Aug 20, 2010 at 10:56:57AM -0500, Anthony Liguori wrote:
>    
> > The real problem is how we do reset.  We shouldn't register a reset
> > handler for every qdev device but rather register a single reset handler
> > that walks the device tree and calls reset on every reachable device.
> >
> > Then we can always call reset in init() and there's no need to have a
> > dev->hotplugged check.  The qdev device tree reset handler should not be
> > registered until *after* we call qemu_system_reset() after creating the
> > device model which will ensure that we don't do a double reset.
> >      
> I don't see why you re-invent the patch.
> Please see the patches I sent out on August 5.
> http://lists.nongnu.org/archive/html/qemu-devel/2010-08/msg00377.html
> http://lists.nongnu.org/archive/html/qemu-devel/2010-08/msg00383.html
>    

I honestly didn't connect the two but it's now obvious to me that they 
overlap significantly.

> Maybe we can merge the patches.
> As for your patch, I have some comment.
> - bus itself may want its own handler. At lease pci bus needs it.
>    And propagating reset signal to children is up to the bus controller.
>    

I disagree.  Reset should be equivalent to power off + init and it's not 
something that can be selectively propagated.

There are different types of bus level resets and it may make sense to 
model that in the PCI layer but the qdev reset is a power cycle 
semantically.

I think using a walker pattern is a stronger design than having each 
reset function do it's own transversal because the later has the 
potential to introduce bugs.

Regards,

Anthony Liguori

> - child devices should be reset before parent.
>    This doesn't matter much though.
>
>