From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MndOK-0006R3-JK for qemu-devel@nongnu.org; Tue, 15 Sep 2009 15:08:40 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MndOJ-0006QO-Jn for qemu-devel@nongnu.org; Tue, 15 Sep 2009 15:08:39 -0400 Received: from [199.232.76.173] (port=41853 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MndOI-0006QH-M1 for qemu-devel@nongnu.org; Tue, 15 Sep 2009 15:08:38 -0400 Received: from ey-out-1920.google.com ([74.125.78.144]:55832) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MndOI-0008DD-5x for qemu-devel@nongnu.org; Tue, 15 Sep 2009 15:08:38 -0400 Received: by ey-out-1920.google.com with SMTP id 13so990356eye.14 for ; Tue, 15 Sep 2009 12:08:36 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <4AAF40FD.5020205@redhat.com> References: <1252943364-32705-1-git-send-email-kraxel@redhat.com> <1252943364-32705-9-git-send-email-kraxel@redhat.com> <4AAF40FD.5020205@redhat.com> From: Blue Swirl Date: Tue, 15 Sep 2009 22:08:16 +0300 Message-ID: Subject: Re: [Qemu-devel] [PATCH 8/9] isa: refine irq reservations Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: qemu-devel@nongnu.org On Tue, Sep 15, 2009 at 10:23 AM, Gerd Hoffmann wrote: > On 09/14/09 18:55, Blue Swirl wrote: >> >> On Mon, Sep 14, 2009 at 6:49 PM, Gerd Hoffmann =C2=A0= wrote: >>> >>> There are a few cases where IRQ sharing on the ISA bus is used and >>> possible. =C2=A0In general only devices of the same kind can do that. >>> A few use cases: >>> >>> =C2=A0* serial lines 1+3 share irq 4 >>> =C2=A0* serial lines 2+4 share irq 3 >>> =C2=A0* parallel ports share irq 7 >>> =C2=A0* 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. =C2=A0So scratch this and maybe use a 'sharing the irq is is fin= e 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. =C2=A0There are= cases > where it works fine (see the list above). =C2=A0It isn't true in general = though. > =C2=A0You can't configure two random devices (say sb16 + ne2k) to share t= he same > irq and expect everything to work fine. I wonder if the PREP machine is emulated correctly. I couldn't find docs about PREP NVRAM or RTC.