From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MGeUK-0001DG-Ut for qemu-devel@nongnu.org; Tue, 16 Jun 2009 15:38:32 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MGeUG-0001Cv-Ia for qemu-devel@nongnu.org; Tue, 16 Jun 2009 15:38:32 -0400 Received: from [199.232.76.173] (port=57997 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MGeUG-0001Cr-BN for qemu-devel@nongnu.org; Tue, 16 Jun 2009 15:38:28 -0400 Received: from mx20.gnu.org ([199.232.41.8]:52450) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MGeUG-00041r-1x for qemu-devel@nongnu.org; Tue, 16 Jun 2009 15:38:28 -0400 Received: from mail.codesourcery.com ([65.74.133.4]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MGeUF-00021e-3K for qemu-devel@nongnu.org; Tue, 16 Jun 2009 15:38:27 -0400 From: Paul Brook Subject: Re: [Qemu-devel] [PATCH] Register usb-uhci reset function. Date: Tue, 16 Jun 2009 20:38:24 +0100 References: <20090616124702.GS19508@redhat.com> <200906161941.06191.paul@codesourcery.com> <20090616191148.GI782@redhat.com> In-Reply-To: <20090616191148.GI782@redhat.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200906162038.25324.paul@codesourcery.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: qemu-devel@nongnu.org >What about the mantra that we should be as close to HW as possible? >Reseting state only on a bus level will not work for hot-unplug anyway Real hardware consists of electrical signals. Qemu emulates the logical effects of a device/subsystem, often at a much higher level. Thus "close to HW as possible" is no longer a straightforward concept. Apart from anything else, I'm pretty sure than on all real hotplug PCI systems each socket is on its own PCI bus to allow electrical isolation of the device before physical hotplug occurs. > > However having the device explicit set its IRQ line during a full system > > reset is a different matter. This is probably harmless most of the time, > > and may paper over other bugs (e.g. the PCI bus not being reset > > properly). However I do not believe it is the correct justification for > > these changes. > > The IRQ state inside piix3 code is QEMU implementation detail. There is > now such thing on real HW. Yes there is. It's a long strip of copper wire with a pullup resistor on the end. Paul