Patchwork Streamline CPU_ADDR_BITS usage

On Mon, Oct 04, 2010 at 01:19:07AM +0200, Peter Stuge wrote:
> Stefan Reinauer wrote:
> > > +config CPU_ADDR_BITS_MASK
> > 
> > Such stuff belongs into an include file, not into Kconfig.
> 
> Good point! I agree completely if it works in practise.

Are you guys suggesting something like this?


I guess that would work, but I'm not sure if that's really a better place for
the code or whether it looks more elegant than in a Kconfig file:

+config CPU_ADDR_BITS_MASK
+       hex
+       default 0x00000000 if CPU_ADDR_BITS_32
+       default 0x0000000f if CPU_ADDR_BITS_36
+       default 0x000000ff if CPU_ADDR_BITS_40
+       default 0x0000ffff if CPU_ADDR_BITS_48
+       help
+         Map the number of address space bits supported by the CPU to the
+         mask field value as it needs to be written into the upper 32 bits
+         of the various MTRRphysMask_MSR MSRs.

Also, if the variable is defined in a header file it should probably not have
the CONFIG_ prefix in the name right? I.e. CPU_ADDR_BITS_MASK, not
CONFIG_CPU_ADDR_BITS_MASK. Which IMHO is also a bit odd, as it _is_ indeed a
value derived from a (not user-visible) kconfig option.


Uwe.

> On Mon, Oct 04, 2010 at 01:19:07AM +0200, Peter Stuge wrote:
> > Stefan Reinauer wrote:
> > > > +config CPU_ADDR_BITS_MASK
> > >
> > > Such stuff belongs into an include file, not into Kconfig.
> >
> > Good point! I agree completely if it works in practise.
> 
> Are you guys suggesting something like this?
> 
> Index: src/include/cpu/cpu.h
> ===================================================================
> --- src/include/cpu/cpu.h       (Revision 5909)
> +++ src/include/cpu/cpu.h       (Arbeitskopie)
> @@ -27,4 +27,21 @@
>  /** end of compile time generated pci driver array */
>  extern struct cpu_driver ecpu_drivers[];
>
> +/*
> + * Map the number of address space bits supported by the CPU to the
> + * mask field value as it needs to be written into the upper 32 bits
> + * of the various MTRRphysMask_MSR MSRs.
> + */
> +#if defined(CONFIG_CPU_ADDR_BITS) && (CONFIG_CPU_ADDR_BITS == 32)
> +#define CONFIG_CPU_ADDR_BITS_MASK 0x00000000
> +#elif defined(CONFIG_CPU_ADDR_BITS) && (CONFIG_CPU_ADDR_BITS == 36)
> +#define CONFIG_CPU_ADDR_BITS_MASK 0x0000000f
> +#elif defined(CONFIG_CPU_ADDR_BITS) && (CONFIG_CPU_ADDR_BITS == 40)
> +#define CONFIG_CPU_ADDR_BITS_MASK 0x000000ff
> +#elif defined(CONFIG_CPU_ADDR_BITS) && (CONFIG_CPU_ADDR_BITS == 48)
> +#define CONFIG_CPU_ADDR_BITS_MASK 0x0000ffff
> +#else
> +#error No CPU_ADDR_BITS value was selected or an unknown value was
> selected
> +#endif
> +
>  #endif /* CPU_CPU_H */

I have no idea what others were envisioning, but I would think something
like this would work for me.

In a processor-specific file:
#define CPU_ADDR_BITS 40

In cpu.h:
#define CPU_ADDR_BITS_MASK (0xffff >> (48 - CPU_ADDR_BITS))

or for the future:
#define CPU_ADDR_BITS_MASK (0xffffff >> (56 - CPU_ADDR_BITS))

Thanks,
Myles