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Re: [Qemu-devel] [PATCH 23/27] hw/core/or-irq: Support more than 16 inpu

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 23/27] hw/core/or-irq: Support more than 16 inputs to an OR gate
Date: Wed, 30 May 2018 18:59:42 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

On 21/05/2018 17:02, Peter Maydell wrote:
> On 21 May 2018 at 15:34, Paolo Bonzini <address@hidden> wrote:
>> Why do the levels have to be migrated at all?  It should be enough if
>> the IRQ level is either migrated manually, or restored (e.g. in
>> post_save callbacks) through other data that is migrated.
> This is standard behaviour for devices: they track their
> inbound irq/gpio lines, and then that becomes internal state for
> them that must be migrated.

But or_irq's input are another device's outbound lines, so tracking them
should not be necessary.  The other device would do it for or_irq.


> If we didn't migrate the input line state, then after a migration
> the levels[] array would be all zeroes, and the next time a
> connected device signalled a high-to-low transition we'd take
> the output line low even if it should not be (because we'd have
> forgotten that some other input lines were high).
> In a different world, the state would be in the qemu_irq line itself
> (in the same way that in hardware signal lines are their own state),
> but we can't get there from here.

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