From: "Michael S. Tsirkin" <mst@redhat.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: linux-s390@vger.kernel.org, markver@us.ibm.com,
Xie Yongji <xieyongji@bytedance.com>,
qemu-devel@nongnu.org, linux-kernel@vger.kernel.org,
Halil Pasic <pasic@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Raphael Norwitz <raphael.norwitz@nutanix.com>,
stefanha@redhat.com, virtualization@lists.linux-foundation.org
Subject: Re: [RFC PATCH 1/1] virtio: write back features before verify
Date: Tue, 5 Oct 2021 07:20:20 -0400 [thread overview]
Message-ID: <20211005072006-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <87lf372084.fsf@redhat.com>
On Tue, Oct 05, 2021 at 01:13:31PM +0200, Cornelia Huck wrote:
> On Tue, Oct 05 2021, Halil Pasic <pasic@linux.ibm.com> wrote:
>
> > On Mon, 4 Oct 2021 05:07:13 -0400
> > "Michael S. Tsirkin" <mst@redhat.com> 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.
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next prev parent reply other threads:[~2021-10-05 11:20 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-30 1:20 [RFC PATCH 1/1] virtio: write back features before verify Halil Pasic
2021-09-30 8:04 ` Christian Borntraeger
2021-09-30 9:28 ` Cornelia Huck
2021-09-30 11:03 ` Halil Pasic
2021-09-30 11:31 ` Cornelia Huck
2021-10-01 14:22 ` Halil Pasic
2021-10-01 15:18 ` Cornelia Huck
2021-10-02 18:13 ` Michael S. Tsirkin
2021-10-04 2:23 ` Halil Pasic
2021-10-04 9:07 ` Michael S. Tsirkin
2021-10-05 10:06 ` Cornelia Huck
2021-10-05 10:43 ` Halil Pasic
2021-10-05 11:11 ` Michael S. Tsirkin
2021-10-05 11:13 ` Cornelia Huck
2021-10-05 11:20 ` Michael S. Tsirkin [this message]
2021-10-05 11:59 ` Halil Pasic
2021-10-05 15:25 ` Cornelia Huck
2021-10-04 7:01 ` Cornelia Huck
2021-10-04 9:25 ` Halil Pasic
2021-10-04 9:51 ` Cornelia Huck
2021-10-02 12:09 ` Michael S. Tsirkin
2021-09-30 11:12 ` Michael S. Tsirkin
2021-09-30 11:36 ` Cornelia Huck
2021-10-02 18:20 ` Michael S. Tsirkin
2021-10-03 5:00 ` Halil Pasic
2021-10-03 6:42 ` Michael S. Tsirkin
2021-10-03 7:26 ` Michael S. Tsirkin
2021-10-04 12:01 ` Cornelia Huck
2021-10-04 12:54 ` Michael S. Tsirkin
2021-10-04 14:27 ` Cornelia Huck
2021-10-04 15:05 ` Michael S. Tsirkin
2021-10-04 15:45 ` [virtio-dev] " Cornelia Huck
2021-10-04 20:01 ` Michael S. Tsirkin
2021-10-05 7:38 ` Cornelia Huck
2021-10-05 11:17 ` Halil Pasic
2021-10-05 11:22 ` Michael S. Tsirkin
2021-10-05 15:20 ` Cornelia Huck
2021-10-01 7:21 ` Halil Pasic
2021-10-02 10:21 ` Michael S. Tsirkin
2021-10-04 12:19 ` Cornelia Huck
2021-10-04 13:11 ` Michael S. Tsirkin
2021-10-04 14:33 ` Cornelia Huck
2021-10-04 15:07 ` Michael S. Tsirkin
2021-10-04 15:50 ` Cornelia Huck
2021-10-04 19:17 ` Michael S. Tsirkin
2021-10-06 10:13 ` Cornelia Huck
2021-10-06 12:15 ` Michael S. Tsirkin
2021-10-05 7:25 ` Halil Pasic
2021-10-05 7:53 ` Michael S. Tsirkin
2021-10-05 10:46 ` Halil Pasic
2021-10-05 11:11 ` Michael S. Tsirkin
2021-10-01 14:34 ` Christian Borntraeger
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