Maciej W. Rozycki <macro@xxxxxxxxxxxxxx> writes: > On Fri, 16 Jan 2015, Markos Chandras wrote: > > > GCC versions supporting MIPS R6 use the ZC constraint to enforce a > > 9-bit offset for MIPS R6. We will use that for all MIPS R6 LL/SC > > instructions. > > > > Cc: Matthew Fortune <Matthew.Fortune@xxxxxxxxxx> > > Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx> > > --- > > arch/mips/include/asm/compiler.h | 10 +++++++++- > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > diff --git a/arch/mips/include/asm/compiler.h > b/arch/mips/include/asm/compiler.h > > index c73815e0123a..8f8ed0245a09 100644 > > --- a/arch/mips/include/asm/compiler.h > > +++ b/arch/mips/include/asm/compiler.h > > @@ -16,12 +16,20 @@ > > #define GCC_REG_ACCUM "accum" > > #endif > > > > +#ifdef CONFIG_CPU_MIPSR6 > > +/* > > + * GCC uses ZC for MIPS R6 to indicate a 9-bit offset although > > + * the macro name is a bit misleading > > + */ > > +#define GCC_OFF12_ASM() "ZC" > > +#else > > #ifndef CONFIG_CPU_MICROMIPS > > #define GCC_OFF12_ASM() "R" > > #elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9) > > #define GCC_OFF12_ASM() "ZC" > > #else > > #error "microMIPS compilation unsupported with GCC older than 4.9" > > -#endif > > +#endif /* CONFIG_CPU_MICROMIPS */ > > +#endif /* CONFIG_CPU_MIPSR6 */ > > > > #endif /* _ASM_COMPILER_H */ > > I'd prefer to have a GCC version trap here just like with the microMIPS > constraint. What is the first upstream version to support R6? 5.0? Correct. > Also rather than stating that the name of the macro has now become a > misnomer I think it should actually be renamed to something more general, > like `GCC_OFF_SMALL_ASM' (any better suggestions are welcome). That'd > have to be a separate patch though, to be applied first, preferably. The ZC constraint is suitable for use in LL/SC/PREF/CACHE for all ISAs. I believe this is the smallest width displacement for a memory operation in all ISAs. The only other reduced displacement in Release 6 is for copro 2 load/stores which are 11-bit rather than 9-bit. Matthew
