Markos Chandras <Markos.Chandras@xxxxxxxxxx> writes: > On 01/20/2015 09:11 AM, Matthew Fortune wrote: > > 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. > > We have tools out there based on 4.9. If we make gcc < 5.0 to fail with > R6, then nobody will be able to build it until 5.0 is released. > Perhaps it makes sense to add some checks in arch/mips/Makefile, see if > our gcc supports -mips32r6 or something and then decide what to do. Indeed, I think it is worthwhile supporting the use of tools which have R6 backported to them owing to long lead times for new versions of GCC to be released. I think you could actually just switch the check around and remove the check for micromips entirely, putting the GCC 4.9 check first: #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9) #define GCC_OFF12_ASM() "ZC" #else #define GCC_OFF12_ASM() "R" #endif >From what I can see this is safe. It was presumably written with a micromips check out of caution to not change older non-micromips code-gen but that doesn't seem particularly important. It is an improvement to older code if anything. Matthew
