Re: [qemu-s390x] [PATCH 12/15] s390-bios: Refactor virtio to run channel programs via cio

[Jason J. Herne]

On 12/14/18 8:04 AM, Cornelia Huck wrote:
> On Wed, 12 Dec 2018 09:11:15 -0500
> "Jason J. Herne" <address@hidden> wrote:
>
> > Now that we have a Channel I/O library let's modify virtio boot code to
> > make use of it for running channel programs.
> >
> > Signed-off-by: Jason J. Herne <address@hidden>
> > ---
> >   pc-bios/s390-ccw/virtio.c | 21 ++-------------------
> >   1 file changed, 2 insertions(+), 19 deletions(-)
> >
> > diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c
> > index aa9da72..5fb49e2 100644
> > --- a/pc-bios/s390-ccw/virtio.c
> > +++ b/pc-bios/s390-ccw/virtio.c
> > @@ -92,30 +92,13 @@ int drain_irqs(SubChannelId schid)
> >   static int run_ccw(VDev *vdev, int cmd, void *ptr, int len)
> >   {
> >       Ccw1 ccw = {};
> > -    CmdOrb orb = {};
> > -    int r;
> > -
> > -    enable_subchannel(vdev->schid);
> > -
> > -    /* start subchannel command */
> > -    orb.fmt = 1;
> > -    orb.cpa = (u32)(long)&ccw;
> > -    orb.lpm = 0x80;
> >   
> >       ccw.cmd_code = cmd;
> >       ccw.cda = (long)ptr;
> >       ccw.count = len;
> >   
> > -    r = ssch(vdev->schid, &orb);
> > -    /*
> > -     * XXX Wait until device is done processing the CCW. For now we can
> > -     *     assume that a simple tsch will have finished the CCW processing,
> > -     *     but the architecture allows for asynchronous operation
> > -     */
> > -    if (!r) {
> > -        r = drain_irqs(vdev->schid);
> > -    }
> > -    return r;
> > +    enable_subchannel(vdev->schid);
>
> Preexisting, but I'm wondering why we enable the subchannel here and
> not just once?
>
> > +    return do_cio(vdev->schid, ptr2u32(&ccw), CCW_FMT1);
> >   }
> >   
> >   static void vring_init(VRing *vr, VqInfo *info)

Good question. It seems to be needed for the net-boot path. Here is the chain:

netmain.c : main()
netmain,c : net_init()
virtio-net.c : virtio_net_init()
virtio.c : virtio_setup_ccw()
virtio.c : run_ccw()

In this case the subchannel would not already be enabled. I suppose I *could* change it, 
but at this point I'm trying to limit how much more code I'm touching :). This patch set 
already touches a bit more code than I anticipated. Let me know what your thoughts are.

--
-- Jason J. Herne (address@hidden)