[PATCH 3/8] ARM: make xscale iwmmxt code multiplatform aware

[Russell King - ARM Linux]

On Wed, Mar 04, 2015 at 03:38:29PM +0100, Arnd Bergmann wrote:
> On Wednesday 04 March 2015 15:12:02 Robert Jarzmik wrote:
> > Arnd Bergmann <arnd at arndb.de> writes:
> 
> > 
> > I'm not sure I understand this patch fully, so take with caution my comment.
> > If I'm not mistaken, the former behavior was for pxa3xx:
> >  - cpu_is_xscale() -> false
> >  - cpu_is_xsc3() -> true
> >  => this implied PMD_BIT4 was set
> > 
> > With your patch :
> >  - cpu_is_xscale() -> true
> >  - cpu_is_xsc3() -> true
> >  => this implied PMD_BIT4 is not set
> > 
> > I like the new meaning for cpu_is_*(), but is the change of PMD_BIT4 the goal of
> > this patch (the piece in [1]) ?
> 
> > > -     if (cpu_architecture() <= CPU_ARCH_ARMv5TEJ && !cpu_is_xscale())
> > > +     if (cpu_architecture() <= CPU_ARCH_ARMv5TEJ &&
> > > +         !cpu_is_xscale() && !cpu_is_xsc3())
> > >               prot |= PMD_BIT4;
> > >  
> > >       pgd += pgd_index(addr);
> 
> I tried to not change the behavior here, and I think you missed this part:
> 
> -#if !defined(CONFIG_CPU_XSCALE) && !defined(CONFIG_CPU_XSC3)
> +#if !defined(CONFIG_CPU_XSCALE)
>  #define        cpu_is_xscale() 0
>  #else
> -#define        cpu_is_xscale() 1
>  ...
> 
> This means that previously, cpu_is_xscale() returned true for pxa3xx,
> while now it returns false, and I added the "&& !cpu_is_xsc3()" to
> keep the logic the same as before.

Please don't do stuff like this.  It's really easy for it to be buggy.

Before your change, cpu_is_xscale() returns true for _any_ Xscale CPU,
whether it's v1, v2 or v3.  After your change, it only returns true for
v1 and v2 CPUs.  So now the macro is mis-named, and is misleading.

Either rename the macro, or keep the existing behaviour, or do something
smarter like:

#define cpu_is_xscale() (cpu_is_xsc1_2() || cpu_is_xsc3())

defining cpu_is_xsc1_2() to be your new version of cpu_is_xscale().

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