From: Rusty Russell Subject: Re: [PATCH RFC] virtio-pci: support config layout in BAR1 Date: Fri, 07 Jun 2013 11:43:01 +0930 Message-ID: <87fvwur7ma.fsf@rustcorp.com.au> References: <20130605163500.GA3393@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130605163500.GA3393@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" , Stephen Hemminger , Jason Wang , Paolo Bonzini , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org List-Id: virtualization@lists.linuxfoundation.org "Michael S. Tsirkin" writes: > Some setups don't support enabling BAR0 (IO BAR). Reasons range from CPU > limitations (e.g. on some powerpc setups) to architecture limmitations > (e.g. a setup with >15 PCI bridges, with one virtio device behind each, > on x86). > > PCI Express spec made IO optional, so future guests will disable IO for > a device in more and more configurations. > > This patch makes it possible for host to mirror the config in BAR1, such > that these setups can work properly. > > Guests with old drivers can't be fixed, they will continue to work as > well (or as bad) as they did previously. For this reason, changing > revision id appears unnecessary - it would break setups that previously > worked, partially. > > Future work on re-organizing layout won't conflict with this patch - it > can use a different BAR or put config at an offset, or update revision. > > Signed-off-by: Michael S. Tsirkin Since QEMU won't support this, I think we'll have to wait for the PCI capabilities, ie. the virtio spec 1.0. Cheers, Rusty.