From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MnSOS-00041x-QT for qemu-devel@nongnu.org; Tue, 15 Sep 2009 03:24:04 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MnSON-0003th-2G for qemu-devel@nongnu.org; Tue, 15 Sep 2009 03:24:03 -0400 Received: from [199.232.76.173] (port=44156 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MnSOM-0003te-Vf for qemu-devel@nongnu.org; Tue, 15 Sep 2009 03:23:59 -0400 Received: from mx20.gnu.org ([199.232.41.8]:17128) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MnSOM-00053p-Fj for qemu-devel@nongnu.org; Tue, 15 Sep 2009 03:23:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MnSOK-0008NU-Tx for qemu-devel@nongnu.org; Tue, 15 Sep 2009 03:23:57 -0400 Message-ID: <4AAF40FD.5020205@redhat.com> Date: Tue, 15 Sep 2009 09:23:41 +0200 From: Gerd Hoffmann MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 8/9] isa: refine irq reservations References: <1252943364-32705-1-git-send-email-kraxel@redhat.com> <1252943364-32705-9-git-send-email-kraxel@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Blue Swirl Cc: qemu-devel@nongnu.org On 09/14/09 18:55, Blue Swirl wrote: > On Mon, Sep 14, 2009 at 6:49 PM, Gerd Hoffmann wrote: >> There are a few cases where IRQ sharing on the ISA bus is used and >> possible. In general only devices of the same kind can do that. >> A few use cases: >> >> * serial lines 1+3 share irq 4 >> * serial lines 2+4 share irq 3 >> * parallel ports share irq 7 >> * ppc/prep: ide ports share irq 13 > > There is another ppc/prep case where RTC and m48t59 share irq 8. The > attached patch converts m48t59 to ISA and makes this more visible. Hmm, ok. So scratch this and maybe use a 'sharing the irq is is fine with me' flag instead? > Does sharing of IRQs really have to be fatal? Wasn't ISA bus edge > triggered and so IRQ sharing was a bit unreliable (but not completely > broken) also on real HW? Well, the fundamental problem is that (1) the drivers must be prepared to handle that and (b) the hardware must be designed sanely. There are cases where it works fine (see the list above). It isn't true in general though. You can't configure two random devices (say sb16 + ne2k) to share the same irq and expect everything to work fine. cheers, Gerd