Re: [Qemu-devel] Re: [PATCH 0/5] RFC: distinguish warm reset from cold reset.

[Blue Swirl]

On Mon, Aug 30, 2010 at 11:19 AM, Gleb Natapov <address@hidden> wrote:
> On Mon, Aug 30, 2010 at 05:35:20PM +0900, Isaku Yamahata wrote:
>> On Mon, Aug 30, 2010 at 10:59:19AM +0300, Avi Kivity wrote:
>> >  On 08/30/2010 10:49 AM, Isaku Yamahata wrote:
>> >> This patch set distinguish warm reset from cold reset by
>> >> introducing warm reset callback handler.
>> >> The first 4 patches are trivial clean up patches. The last patch of 5/5
>> >> is RFC patch.
>> >>
>> >> The following thread arose cold reset vs warm reset issues.
>> >> http://lists.nongnu.org/archive/html/qemu-devel/2010-08/msg00186.html
>> >> The summary is
>> >> - warm reset is wanted in qemu
>> >>    - Pressing the reset button is a warm reset on real machines
>> >>    - Sparc64 CPU uses different reset vector for warm and cold reset,
>> >>      so system_reset acts like a reset button
>> >>    - Bus reset can be implemented utilizing qdev frame work instead of
>> >>      implemeting it each bus layer independently.
>> >> - The modification should be incremental.
>> >>    Anthony would like to see that as an incremental addition to what we 
>> >> have
>> >>    today (like introducing a propagating warm reset callback) and thinking
>> >>    through what the actual behavior should and shouldn't be.
>> >>
>> >>
>> >> If the direction is okay, The next step would be a patch(set) for qdev 
>> >> which
>> >> would introduce qdev_cold_reset(), qdev_warm_reset(),
>> >> DeviceInfo::cold_reset and DeviceInfo::warm_reset
>> >> and would obsolete qdev_reset() and DeviceInfo::reset.
>> >>
>> >
>> > What would be the difference between warm and cold reset?  Former called
>> > on any reset, while the latter called on power up only?
>>
>> What I have in mind at the moment is,
>> warm reset callback is called on warm reset, not called on power up.
>> cold reset callback is called only on power up (and power cycle).
>>
> Why stop there. Why not implement proper power planes support. Some
> devices are not powered down on S3/S4 suspend for instance.

Is warm reset similar to what happens to these when resuming from
suspend? Or is there some additional signal to tell the device? Is
there a spec for these things?