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

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 12 Dec 2018 09:11:15 -0500
"Jason J. Herne" <jjherne@linux.ibm.com> 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 <jjherne@linux.ibm.com>
> ---
>  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)