Re: [Qemu-devel] [PATCH v2 04/11] acpi: add aml_concatenate()

[Xiao Guangrong]

On 02/15/2016 05:02 PM, Igor Mammedov wrote:
> On Sun, 14 Feb 2016 13:55:24 +0800
> Xiao Guangrong <address@hidden> wrote:
>
> > On 02/14/2016 01:52 PM, Xiao Guangrong wrote:
> > > On 02/08/2016 06:51 PM, Igor Mammedov wrote:
> > > > On Wed, 13 Jan 2016 02:50:03 +0800
> > > > Xiao Guangrong <address@hidden> wrote:
> > > >
> > > > > It will be used by nvdimm acpi
> > > > >
> > > > > Signed-off-by: Xiao Guangrong <address@hidden>
> > > > > ---
> > > > >    hw/acpi/aml-build.c         | 14 ++++++++++++++
> > > > >    include/hw/acpi/aml-build.h |  1 +
> > > > >    2 files changed, 15 insertions(+)
> > > > >
> > > > > diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
> > > > > index 97c9efb..421dd84 100644
> > > > > --- a/hw/acpi/aml-build.c
> > > > > +++ b/hw/acpi/aml-build.c
> > > > > @@ -1440,6 +1440,20 @@ Aml *aml_alias(const char *source_object, const char 
> > > > > *alias_object)
> > > > >        return var;
> > > > >    }
> > > > >
> > > > > +/* ACPI 1.0b: 16.2.5.4 Type 2 Opcodes Encoding: DefConcat */
> > > > > +Aml *aml_concatenate(Aml *source1, Aml *source2, Aml *target)
> > > > > +{
> > > > > +    Aml *var = aml_opcode(0x73 /* ConcatOp */);
> > > > > +    aml_append(var, source1);
> > > > > +    aml_append(var, source2);
> > > > > +
> > > > > +    if (target) {
> > > > > +        aml_append(var, target);
> > > > > +    }
> > > > target is not an optional, pls looks at aml_add and use
> > > > helper to make patch correct and smaller
> > >
> > > Indeed, i will change it to:
> > >
> > > /* ACPI 1.0b: 16.2.5.4 Type 2 Opcodes Encoding: DefConcat */
> > > Aml *aml_concatenate(Aml *source1, Aml *source2, Aml *target)
> > > {
> > >       return  build_opcode_2arg_dst(0x73 /* ConcatOp */, arg1, arg2, dst);
> > > }
> >
> > And make a assert for @target to ensure it can not be NULL.
> Don't do that, see build_opcode_2arg_dst(), target can be NULL
> that allows to express implicit target like:
>
>    aml_add(a, aml_add(b, c, NULL), NULL)
>
> where one doesn't need an intermediate variable to store result.

Yes, you are right, i re-checked the spec and it said that "Source2 is
concatenated to Source1 and the result data is optionally stored into Result" 
so that
@target can be eliminated.