linux-kernel - Re: [PATCH v2] m68k: math-emu: Fix dependencies of math emulation support

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Message-ID: <551618d4-f384-47a9-39c4-9ec3c636a06d@linux-m68k.org>
Date:   Mon, 16 May 2022 16:06:54 +1000
From:   Greg Ungerer <gerg@...ux-m68k.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     kernel test robot <lkp@...el.com>, linux-m68k@...ts.linux-m68k.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] m68k: math-emu: Fix dependencies of math emulation
 support

Hi Geert,

On 13/5/22 22:50, Geert Uytterhoeven 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 M68KCLASSIC (to rule out Coldfire) and FPU (kernel
> has some type of floating-point support --- be it hardware or software
> emulated, to rule out anything 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>

Reviewed-by: Greg Ungerer <gerg@...ux-m68k.org>

Regards
Greg



> ---
> To be queued in the m68k for-v5.19 branch.
> 
> v2:
>    - Fix typo in M68KCLASSIC,
>    - Improve rationale behind FPU dependency.
> ---
>   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..3d5da25c73b5af8a 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 M68KCLASSIC && FPU
>   	help
>   	  At some point in the future, this will cause floating-point math
>   	  instructions to be emulated by the kernel on machines that lack a