From mboxrd@z Thu Jan 1 00:00:00 1970 From: Farhan Ali Subject: Re: [PATCH 1/3] vfio-ccw: add capabilities chain Date: Tue, 27 Nov 2018 14:04:49 -0500 Message-ID: References: <20181122165432.4437-1-cohuck@redhat.com> <20181122165432.4437-2-cohuck@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-s390@vger.kernel.org, qemu-s390x@nongnu.org, Alex Williamson , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Cornelia Huck , Halil Pasic , Eric Farman , Pierre Morel Return-path: In-Reply-To: <20181122165432.4437-2-cohuck@redhat.com> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org 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 > * Xiao Feng Ren > + * Cornelia Huck > */ > > #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? :)