Re: [Xen-devel] [PATCH v3 1/2] atomic: add atomic_and operations

[Julien Grall <julien@xxxxxxx>]

Hi,

On 24/02/2020 10:23, Roger Pau Monné wrote:
> On Mon, Feb 24, 2020 at 10:19:44AM +0000, Julien Grall wrote:
> > Hi,
> >
> > On 24/02/2020 10:09, Roger Pau Monné wrote:
> > > On Mon, Feb 24, 2020 at 10:02:53AM +0000, Julien Grall wrote:
> > > > Hi Roger,
> > > >
> > > > The logic for Arm64 and Arm32 looks good to me. I just have one question
> > > > below.
> > > >
> > > > On 24/02/2020 08:43, Roger Pau Monne wrote:
> > > > > To x86 and Arm. This performs an atomic AND operation against an
> > > > > atomic_t variable with the provided mask.
> > > > >
> > > > > Requested-by: Jan Beulich <jbeulich@xxxxxxxx>
> > > > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > > > ---
> > > > >     xen/include/asm-arm/arm32/atomic.h | 17 +++++++++++++++++
> > > > >     xen/include/asm-arm/arm64/atomic.h | 14 ++++++++++++++
> > > > >     xen/include/asm-x86/atomic.h       |  8 ++++++++
> > > > >     3 files changed, 39 insertions(+)
> > > > >
> > > > > diff --git a/xen/include/asm-arm/arm32/atomic.h 
> > > > > b/xen/include/asm-arm/arm32/atomic.h
> > > > > index c03eb684cd..4637381bcc 100644
> > > > > --- a/xen/include/asm-arm/arm32/atomic.h
> > > > > +++ b/xen/include/asm-arm/arm32/atomic.h
> > > > > @@ -96,6 +96,23 @@ static inline int atomic_sub_return(int i, atomic_t *v)
> > > > >         return result;
> > > > >     }
> > > > > +static inline void atomic_and(unsigned int m, atomic_t *v)
> > > > All the atomic helpers have taken a signed int so far because the counter is
> > > > an int. Any reason to diverge from that?
> > > Since this is not an arithmetic operation I felt unsigned int was a
> > > more suitable type to describe a bitmask: it felt weird to pass a
> > > bitmask with type int, because signedness doesn't make sense when
> > > referring to a mask.
> > At some point I would like to have macro generating all the atomics in on
> > Arm in the same way a Linux (see asm-generic/atomic.h). This is to avoid
> > duplication and make easy to introduce Armv8.1 LSE atomics. So I would like
> > to avoid introducing difference in the prototype unless it is stricly
> > necessary.
> Why not have the macro generator function get passed the type of the
> parameter?
It is not worth it for a simple operation and I don't want to diverge 
too much of atomics from Linux.
Cheers,

--
Julien Grall

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