Re: [Qemu-devel] [PATCH 11/22] i8259: Update IRQ state after reset

[Blue Swirl]

On Wed, Sep 28, 2011 at 9:18 PM, Jan Kiszka <address@hidden> wrote:
> On 2011-09-28 20:01, Blue Swirl wrote:
>>
>> On Wed, Sep 28, 2011 at 11:00 AM, Jan Kiszka<address@hidden>
>>  wrote:
>>>
>>> As we clearly modify the PIC state on pic_reset, we also have to update
>>> the IRQ output. This only happened on init so far. Apply this
>>> consistently.
>>
>> Nack, IRQ lines shouldn't be touched on reset. The other side may not
>> be ready for receiving the interrupt change and qemu_irqs are
>> stateless anyway.
>
> Sorry, but failing to clear the line (this is what pic_update_irq will
> effectively do) is a clear bug in the current code. This patch is 100%
> analogue to what, e.g. the PCI layer does on reset. Please re-read.

Reset will happen also when the devices are created. At that time,
qemu_irq callback triggered by changing of the state may produce
undesired effects on the other side. There have been bugs earlier, see
bc26e55a6615dc594be425d293db40d5cdcdb84b and
42f1ced228c9b616cfa2b69846025271618e4ef5 and discussion in
http://lists.nongnu.org/archive/html/qemu-devel/2009-06/msg01024.html.