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Tsirkin" To: Cornelia Huck Subject: Re: [RFC PATCH 1/1] virtio: write back features before verify Message-ID: <20211005072006-mutt-send-email-mst@kernel.org> References: <87r1d64dl4.fsf@redhat.com> <20210930130350.0cdc7c65.pasic@linux.ibm.com> <87ilyi47wn.fsf@redhat.com> <20211001162213.18d7375e.pasic@linux.ibm.com> <87v92g3h9l.fsf@redhat.com> <20211002082128-mutt-send-email-mst@kernel.org> <20211004042323.730c6a5e.pasic@linux.ibm.com> <20211004040937-mutt-send-email-mst@kernel.org> <20211005124303.3abf848b.pasic@linux.ibm.com> <87lf372084.fsf@redhat.com> MIME-Version: 1.0 In-Reply-To: <87lf372084.fsf@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: linux-s390@vger.kernel.org, markver@us.ibm.com, Xie Yongji , qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, Halil Pasic , Christian Borntraeger , Raphael Norwitz , stefanha@redhat.com, virtualization@lists.linux-foundation.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Tue, Oct 05, 2021 at 01:13:31PM +0200, Cornelia Huck wrote: > On Tue, Oct 05 2021, Halil Pasic wrote: > > > On Mon, 4 Oct 2021 05:07:13 -0400 > > "Michael S. Tsirkin" wrote: > >> Well we established that we can know. Here's an alternative explanation: > > > > > > I thin we established how this should be in the future, where a transport > > specific mechanism is used to decide are we operating in legacy mode or > > in modern mode. But with the current QEMU reality, I don't think so. > > Namely currently the switch native-endian config -> little endian config > > happens when the VERSION_1 is negotiated, which may happen whenever > > the VERSION_1 bit is changed, or only when FEATURES_OK is set > > (vhost-user). > > > > This is consistent with device should detect a legacy driver by checking > > for VERSION_1, which is what the spec currently says. > > > > So for transitional we start out with native-endian config. For modern > > only the config is always LE. > > > > The guest can distinguish between a legacy only device and a modern > > capable device after the revision negotiation. A legacy device would > > reject the CCW. > > > > But both a transitional device and a modern only device would accept > > a revision > 0. So the guest does not know for ccw. > > Well, for pci I think the driver knows that it is using either legacy or > modern, no? > > And for ccw, the driver knows at that point in time which revision it > negotiated, so it should know that a revision > 0 will use LE (and the > device will obviously know that as well.) > > Or am I misunderstanding what you're getting at? Exactly what I'm saying. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization