On Tue, 27 Nov 2018 14:04:49 -0500 Farhan Ali <alifm@xxxxxxxxxxxxx> wrote: > 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@xxxxxxxxxxxxxxxxxx> > > * Xiao Feng Ren<renxiaof@xxxxxxxxxxxxxxxxxx> > > + * Cornelia Huck<cohuck@xxxxxxxxxx> > > */ > > > > #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? :) > My entire reasoning was "hey, vfio-pci is using this, so it should not be bad" 8)
