From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:51461) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLRSm-0008Q8-BZ for qemu-devel@nongnu.org; Tue, 01 Nov 2011 23:26:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RLRSd-0004G7-Jb for qemu-devel@nongnu.org; Tue, 01 Nov 2011 23:26:02 -0400 Received: from ozlabs.org ([203.10.76.45]:52805) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLRSb-0004CW-PD for qemu-devel@nongnu.org; Tue, 01 Nov 2011 23:25:54 -0400 From: Rusty Russell In-Reply-To: <4EB07096.4070806@us.ibm.com> References: <1317360376-12090-1-git-send-email-david@gibson.dropbear.id.au> <4EB07096.4070806@us.ibm.com> Date: Wed, 02 Nov 2011 13:52:55 +1030 Message-ID: <87r51rtdgw.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori , David Gibson Cc: Alexey Kardashevskiy , qemu-devel@nongnu.org, Sasha Levin , "Michael S. Tsirkin" On Tue, 01 Nov 2011 17:20:06 -0500, Anthony Liguori wrote: > On 09/30/2011 12:26 AM, David Gibson wrote: > > Currently, virtio devices are usually presented to the guest as an > > emulated PCI device, virtio_pci. Although the actual IO operations > > are done through system memory, the configuration of the virtio device > > is done through the one PCI IO space BAR that virtio_pci presents. > > > > But PCI IO space (aka PIO) is deprecated for modern PCI devices, and > > on some systems with many PCI domains accessing PIO space can be > > problematic. For example on the existing PowerVM implementation of > > the PAPR spec, PCI PIO access is not supported at all. We're hoping > > that our KVM implementation will support PCI PIO (once we support PCI > > at all), but it will probably have some irritating limitations. > > > > This patch, therefore, extends the virtio_pci device to have a PCI > > memory space (MMIO) BAR as well as the IO BAR. The MMIO BAR contains > > exactly the same registers, in exactly the same layout as the existing > > PIO BAR. > > > > Because the PIO BAR is still present, existing guest drivers should > > still work fine. With this change in place, future guest drivers can > > check for an MMIO BAR and use that if present (falling back to PIO > > when possible to support older qemu versions). > > > > Signed-off-by: David Gibson > > Seems harmless for QEMU, so applied. You should update the virtio-pci spec too. > > Regards, Can you revert this? We just reverted the kernel part, figuring we need a rethink. Thanks, Rusty.