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Re: [Qemu-devel] [PATCH for-2.4 1/2] core: reset handler for bus-less de

From: Andreas Färber
Subject: Re: [Qemu-devel] [PATCH for-2.4 1/2] core: reset handler for bus-less devices
Date: Mon, 13 Jul 2015 17:05:31 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

Am 13.07.2015 um 16:30 schrieb Christian Borntraeger:
> Am 13.07.2015 um 16:20 schrieb Andreas Färber:
>> Am 13.07.2015 um 16:11 schrieb Cornelia Huck:
>>> On Mon, 13 Jul 2015 14:22:05 +0200
>>> Christian Borntraeger <address@hidden> wrote:
>>>> Am 09.07.2015 um 18:51 schrieb Cornelia Huck:
>>>>> Devices that don't live on a bus aren't caught by the normal device
>>>>> reset logic. Let's register a reset handler for those devices during
>>>>> device realization that calls the reset handler for the associated
>>>>> device class.
>>>>> Suggested-by: Peter Crosthwaite <address@hidden>
>>>>> Signed-off-by: Cornelia Huck <address@hidden>
>>>> reboot (from within guest) and external reset (system_reset in monitor)
>>>> now work fine with the s390 watchdog.
>>>> Tested-by: Christian Borntraeger <address@hidden>
>>>>> ---
>>>>>  hw/core/qdev.c | 15 +++++++++++++++
>>>>>  1 file changed, 15 insertions(+)
>>> Thanks.
>>> Any objections against taking this through s390-next? I'd like to fix
>>> diag288 reset (+ that annoying migration regession) for 2.4-rc1 and
>>> send a pull request soon.
>> Which device does this fix (only this diag88?), and is it really not
>> possible to register a reset handler where it's being created?
> A sysbus device reset is also not registered or called by its parent. It is 
> resetted by the generic qdev handler walking all children (qdev_reset_all and 
> qbus_reset_all), no?

It seems you're missing my point.

Having a SysBusDevice reset by the SysBus is the expected way, rather
than having the SysBusDevice register its own handler. Reset propagates
along defined paths - buses and composition - and doesn't hit randomly.
Therefore resetting random bus-less devices is wrong by design. And a
step backwards, too.

Which btw is the reason that my recursive realization patches stalled -
we were potentially violating these rules.

Anyway, here it's not about a SysBusDevice, it's about a pure Device,
unless I've misunderstood something.


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