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Re: [Qemu-devel] [PATCH v4 5/5] i8259: fix dynamically masking slave IRQ


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v4 5/5] i8259: fix dynamically masking slave IRQs with IMR register
Date: Mon, 03 Sep 2012 13:11:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0

Il 03/09/2012 12:34, Jan Kiszka ha scritto:
>> > Why is this a problem?  All of them use IRQ2 for a cascade, and initialize
>> > icw3 to 0x4/0x2 (I checked OpenBIOS, rth's palcode for Alpha, and Linux).
> IRQ2 is already hard-coded in QEMU (we had to patch this for our machine
> emulation, but less in recent versions), that is not the point. I'm
> concerned about the behavioral changes we are discussing here, ie. the
> special handling of cascading interrupt inputs.

Yeah, it's quite interesting that the behavior isn't mentioned in the
8259 datasheets.  Still in retrospect it's hard to see how it can
possibly work with edge-triggered cascaded inputs.

Paolo



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