On 01/20/2015 10:08 AM, Matthew Fortune wrote: > 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 > For non-micromips kernel, this will start using "ZC" instead of "R", whereas before, it only used "ZC" for micromips and "R" for everything else. Is that safe? Maciej was the one committed this code, so if that's still safe, then I will change it as requested. -- markos
