Re: [PATCH 7/8] m68k: only generate FPU instructions of CONFIG_FPU

[Greg Ungerer <gerg@linux-m68k.org>]

Hi Geert,

On 29/08/16 22:53, Geert Uytterhoeven wrote:
> Hi Greg,
> 
> On Mon, Aug 29, 2016 at 1:43 PM, Greg Ungerer <gerg@linux-m68k.org> wrote:
>> Most of the m68k code that supports a hardware FPU is surrounded by
>> CONFIG_FPU. Except this setup code in setup_mm.c. Be consistent and
>> surround these hardware FPU instructions with CONFIG_FPU instead of
>> a check based on CONFIG_M68KFPU_EMU_ONLY.
>>
>> The side effect of this is that we can now compile a kernel with no
>> m68k/ColdFire hardware support FPU instructions at all (if we do not
>> define CONFIG_FPU).
>>
>> Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
>> ---
>>  arch/m68k/kernel/setup_mm.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/m68k/kernel/setup_mm.c b/arch/m68k/kernel/setup_mm.c
>> index 13f4640..00290c4 100644
>> --- a/arch/m68k/kernel/setup_mm.c
>> +++ b/arch/m68k/kernel/setup_mm.c
>> @@ -245,7 +245,7 @@ void __init setup_arch(char **cmdline_p)
>>          * We should really do our own FPU check at startup.
>>          * [what do we do with buggy 68LC040s? if we have problems
>>          *  with them, we should add a test to check_bugs() below] */
>> -#ifndef CONFIG_M68KFPU_EMU_ONLY
>> +#ifdef CONFIG_FPU
>>         /* clear the fpu if we have one */
>>         if (m68k_fputype & (FPU_68881|FPU_68882|FPU_68040|FPU_68060|FPU_COLDFIRE)) {
>>                 volatile int zero = 0;
> 
> This piece of code is now compiled in if CONFIG_M68KFPU_EMU_ONLY=y?

Yes, that is true. In that scenario I would expect m68k_fputype
to be 0. So it wouldn't be executed. 

The problem for me on ColdFire is that we currently do not
support the FPU emulation (the assembler for it is not ColdFire
clean). So in this case here we can't have CONFIG_M68KFPU_EMU_ONLY=y.

Would you prefer if it became:

  #if defined(CONFIG_FPU) && !defined(CONFIG_M68KFPU_EMU_ONL)

For the existing classic m68k machines they always currently
have CONFIG_FPU set. So that would be no change for them. And
for the ColdFire machines that do not have FPU hardware we are
good because CONFIG_FPU won't be set.

Regards
Greg