linux-kernel - Re: [PATCH] m68k: math-emu: Fix dependencies of math emulation support

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Message-ID: <db869491-142f-4360-0f3c-e4395563088b@uclinux.org>
Date:   Fri, 13 May 2022 09:23:11 +1000
From:   Greg Ungerer <gerg@...inux.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] m68k: math-emu: Fix dependencies of math emulation
 support

Hi Geert,

On 11/5/22 22:54, Geert Uytterhoeven wrote:
> On Wed, May 11, 2022 at 11:48 AM Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
>> If CONFIG_M54xx=y, CONFIG_MMU=y, and CONFIG_M68KFPU_EMU=y:
>>
>>      {standard input}:272: Error: invalid instruction for this architecture; needs 68000 or higher (68000 [68ec000, 68hc000, 68hc001, 68008, 68302, 68306, 68307, 68322, 68356], 68010, 68020 [68k, 68ec020], 68030 [68ec030], 68040 [68ec040], 68060 [68ec060], cpu32 [68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349, 68360], fidoa [fido]) -- statement `sub.b %d1,%d3' ignored
>>      {standard input}:609: Error: invalid instruction for this architecture; needs 68020 or higher (68020 [68k, 68ec020], 68030 [68ec030], 68040 [68ec040], 68060 [68ec060]) -- statement `bfextu 4(%a1){%d0,#8},%d0' ignored
>>      {standard input}:752: Error: operands mismatch -- statement `mulu.l 4(%a0),%d3:%d0' ignored
>>      {standard input}:1155: Error: operands mismatch -- statement `divu.l %d0,%d3:%d7' ignored
>>
>> The math emulation support code is intended for 68020 and higher, and
>> uses several instructions or instruction modes not available on coldfire
>> or 68000.
>>
>> Originally, the dependency of M68KFPU_EMU on MMU was fine, as MMU
>> support was only available on 68020 or higher.  But this assumption
>> was broken by the introduction of MMU support for M547x and M548x.
>>
>> Drop the dependency on MMU, as the code should work fine on 68020 and up
>> without MMU (which are not yet supported by Linux, though).
>> Add dependencies on M68K_CLASSIC (to rule out Coldfire) and FPU (to rule
>> out 68xxx below 68020).
>>
>> Fixes: 1f7034b9616e6f14 ("m68k: allow ColdFire 547x and 548x CPUs to be built with MMU enabled")
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> ---
>> To be queued in the m68k for-v5.19 branch.
>>
>>   arch/m68k/Kconfig.cpu | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/m68k/Kconfig.cpu b/arch/m68k/Kconfig.cpu
>> index 16ea9a67723c09dc..9abddbbee819f1d3 100644
>> --- a/arch/m68k/Kconfig.cpu
>> +++ b/arch/m68k/Kconfig.cpu
>> @@ -327,7 +327,7 @@ comment "Processor Specific Options"
>>
>>   config M68KFPU_EMU
>>          bool "Math emulation support"
>> -       depends on MMU
>> +       depends on M68K_CLASSIC && FPU
>                        ^^^^^^^^^^^^
> Whoops, that's a silly typo...

Are you going to resend, or are you thinking of changing the way this is done?

I had thought that CONFIG_FPU enabled meant you had some type of
floating point support in the kernel - be it hardware or software emulated.
So I don't have a problem with this "as is".

Regards
Greg