Re: [PATCH 2/2] powerpc: cleanup hw_irq.h

[Christophe Leroy]

Le 27/08/2019 Ã 20:26, Segher Boessenkool a ÃcritÂ:
> On Tue, Aug 27, 2019 at 07:36:35PM +0200, Christophe Leroy wrote:
> > Le 27/08/2019 Ã 19:29, Segher Boessenkool a ÃcritÂ:
> > > On Tue, Aug 27, 2019 at 10:48:24PM +1000, Nicholas Piggin wrote:
> > > > Christophe Leroy's on August 27, 2019 6:13 pm:
> > > > > +#define wrtee(val)	asm volatile("wrtee %0" : : "r" (val) : "memory")
> > > > > +#define wrteei(val)	asm volatile("wrteei %0" : : "i" (val) :
> > > > > "memory")
> > > >
> > > > Can you implement just one macro that uses __builtin_constant_p to
> > > > select between the imm and reg versions? I forgot if there's some
> > > > corner cases that prevent that working with inline asm i constraints.
> > >
> > > static inline void wrtee(long val)
> > > {
> > > 	asm volatile("wrtee%I0 %0" : : "n"(val) : "memory");
> > > }
> >
> > Great, didn't know that possibility.
> >
> > Can it be used with any insn, for instance with add/addi ?
> > Or with mr/li ?
>
> Any instruction, yes.  %I<n> simply outputs an "i" if operand n is a
> constant integer, and nothing otherwise.

Thinking about it once more, I'm not sure this form is possible, because 
wrteei expect 0 or 1. If someone calls wrtee(MSR_EE); (or any constant 
containing MSR_EE) wrteei 1 is expected. And any constant with MSR_EE 
cleared should result in wrteei 0.

> So
>    asm("add%I2 %0,%1,%2" : "=r"(dst) : "r"(src1), "ri"(src1));

"ri", not "n" as for wrtee ?

Christophe

> works well.  I don't see how you would use it for li/mr...  You can do
>    asm("add%I1 %0,0,%1" : "=r"(dst) : "ri"(src));
> I suppose, but that is not really an mr.
>
> > > (This output modifier goes back to the dark ages, some 2.4 or something).
> >
> > Hope Clang support it ...
>
> I don't know, sorry.  But it is used all over the place, see sfp-machine.h
> for example, so maybe?
>
>
> Segher