On Thu, Jun 06, 2019 at 11:50:06AM +0200, Paul Durrant wrote:
> > -----Original Message-----
> > From: Xen-devel [mailto:xen-devel-boun...@lists.xenproject.org] On Behalf
> > Of Roger Pau Monne
> > Sent: 06 June 2019 10:02
> > To: xen-devel@lists.xenproject.org
> > Cc: Stefano Stabellini <sstabell...@kernel.org>; Wei Liu <w...@xen.org>;
> > Konrad Rzeszutek Wilk
> > <konrad.w...@oracle.com>; George Dunlap <george.dun...@citrix.com>; Andrew
> > Cooper
> > <andrew.coop...@citrix.com>; Ian Jackson <ian.jack...@citrix.com>; Tim
> > (Xen.org) <t...@xen.org>; Julien
> > Grall <julien.gr...@arm.com>; Jan Beulich <jbeul...@suse.com>; Roger Pau
> > Monne <roger....@citrix.com>
> > Subject: [Xen-devel] [PATCH v2 01/12] pci: introduce a devfn field to
> > pci_sbdf_t
> >
> > This is equivalent to the current extfunc field in term of contents.
> >
> > Switch the two current users of extfunc to use devfn instead for
> > correctness.
> >
> > No functional change.
> >
> > Requested-by: Jan Beulich <jbeul...@suse.com>
> > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
> > ---
> > Cc: Andrew Cooper <andrew.coop...@citrix.com>
> > Cc: George Dunlap <george.dun...@eu.citrix.com>
> > Cc: Ian Jackson <ian.jack...@eu.citrix.com>
> > Cc: Jan Beulich <jbeul...@suse.com>
> > Cc: Julien Grall <julien.gr...@arm.com>
> > Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> > Cc: Stefano Stabellini <sstabell...@kernel.org>
> > Cc: Tim Deegan <t...@xen.org>
> > Cc: Wei Liu <w...@xen.org>
> > ---
> > Changes since v1:
> > - New in this version.
> > ---
> > NB: Paul suggested to name the function field fn instead of func, so
> > that it would match the naming of the devfn field. Sadly the func
> > field cannot be aliased to another field using a union because it's a
> > bit field, so the only option is to rename func to fn.
>
> Is that true? Can you not do something like...
>
> union {
> struct {
> uint8_t func : 3,
> dev : 5;
> };
> struct {
> uint8_t fn : 3,
> pad : 5;
> };
> uint8_t extfunc;
> };
>
> ? I'm certainly not seeing any complaints from gcc.
D'oh, right. I was so focused on aliasing the func field only that it
didn't occur to me. I could even do:
union {
struct {
uint8_t func : 3,
dev : 5;
};
struct {
uint8_t fn : 3,
: 5;
};
uint8_t extfunc,
devfn;
};
Let me make sure this works with all compilers and I will send an
updated version of this patch.
Thanks, Roger.
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