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Re: [PATCH] MIPS: Kconfig: microMIPS and SmartMIPS are mutually exclusiv

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] MIPS: Kconfig: microMIPS and SmartMIPS are mutually exclusive
From: "Maciej W. Rozycki" <macro@linux-mips.org>
Date: Tue, 3 Jun 2014 12:18:43 +0100 (BST)
Cc: Markos Chandras <markos.chandras@imgtec.com>, linux-mips@linux-mips.org
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On Tue, 3 Jun 2014, Ralf Baechle wrote:

> > Warning: the 32-bit microMIPS architecture does not support the `smartmips'
> > extension
> > arch/mips/kernel/entry.S:90: Error: unrecognized opcode `mtlhx $24'
> > [...]
> > arch/mips/kernel/entry.S:109: Error: unrecognized opcode `mtlhx $24'
> > 
> > Link: https://dmz-portal.mips.com/bugz/show_bug.cgi?id=1021
> > Reviewed-by: Steven J. Hill <Steven.Hill@imgtec.com>
> > Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
> > ---
> >  arch/mips/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> > index 2fe8e60..ffde3d6 100644
> > --- a/arch/mips/Kconfig
> > +++ b/arch/mips/Kconfig
> > @@ -2063,7 +2063,7 @@ config ARCH_PHYS_ADDR_T_64BIT
> >         def_bool 64BIT_PHYS_ADDR
> >  
> >  config CPU_HAS_SMARTMIPS
> > -   depends on SYS_SUPPORTS_SMARTMIPS
> > +   depends on SYS_SUPPORTS_SMARTMIPS && !CPU_MICROMIPS
> >     bool "Support for the SmartMIPS ASE"
> >     help
> >       SmartMIPS is a extension of the MIPS32 architecture aimed at
> 
> >From a user's perspective that's a bit quirky; a user has to first
> disable CPU_MICROMIPS before he can enable CPU_HAS_SMARTMIPS.  So I
> think this should become a choice statement.

 Do we need this CPU_HAS_SMARTMIPS setting at all?  Can't we just 
save/restore this SmartMIPS ACX register on context switches where 
available (straightforward to detect at the run time) and have the 
relevant pieces of code excluded (#ifdef-ed out or suchlike) on 
non-supported configurations such as microMIPS or MIPS64?

  Maciej

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