Re: [PATCH 1/3] vfio-ccw: add capabilities chain

Farhan Ali
2018-11-27T19:04:49Z

On 11/22/2018 11:54 AM, Cornelia Huck wrote:
> diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
> index 078e46f9623d..a6f9f84526e2 100644
> --- a/drivers/s390/cio/vfio_ccw_private.h
> +++ b/drivers/s390/cio/vfio_ccw_private.h
> @@ -3,9 +3,11 @@
> * Private stuff for vfio_ccw driver
> *
> * Copyright IBM Corp. 2017
> + * Copyright Red Hat, Inc. 2018
> *
> * Author(s): Dong Jia Shi<bjsdjshi@linux.vnet.ibm.com>
> * Xiao Feng Ren<renxiaof@linux.vnet.ibm.com>
> + * Cornelia Huck<cohuck@redhat.com>
> */
>
> #ifndef_VFIO_CCW_PRIVATE_H_
> @@ -19,6 +21,38 @@
> #include "css.h"
> #include "vfio_ccw_cp.h"
>
> +#define VFIO_CCW_OFFSET_SHIFT 40
> +#define VFIO_CCW_OFFSET_TO_INDEX(off) (off >> VFIO_CCW_OFFSET_SHIFT)
> +#define VFIO_CCW_INDEX_TO_OFFSET(index) ((u64)(index) << VFIO_CCW_OFFSET_SHIFT)
> +#define VFIO_CCW_OFFSET_MASK (((u64)(1) << VFIO_CCW_OFFSET_SHIFT) - 1)
> +

Why is the offset shift 40? I know vfio-pci is also using the same
offset shift, but I am curious about the reasoning behind why we are
using this? :)