[PATCH] ARM: let CPUs not being able to run in ARM mode enter in THUMB mode

[u.kleine-koenig@pengutronix.de (Uwe Kleine-König)]

Hi Russell,

On Fri, Jan 11, 2013 at 04:07:53PM +0000, Russell King - ARM Linux wrote:
> On Fri, Jan 11, 2013 at 12:39:57PM +0100, Uwe Kleine-K?nig wrote:
> > +# Select this if your CPU doesn't support the 32 bit ARM instructions.
> > +config THUMBONLY_CPU
> > +	bool
> > +	select THUMB2_KERNEL
> > +	select ARM_THUMB
> 
> Hmm, not convinced this is the best solution.  Yes, fine for there to be
> a THUMBONLY_CPU option, _but_ not the select statements onto user visible
> symbols.  We can get this instead by:
> 
> config THUMB2_KERNEL
>         bool "Compile the kernel in Thumb-2 mode" if !THUMBONLY_CPU
>         depends on (CPU_V7 && !CPU_V6 && !CPU_V6K) || THUMBONLY_CPU
> 	default y if THUMBONLY_CPU
>         select AEABI
>         select ARM_ASM_UNIFIED
>         select ARM_UNWIND
> 
> and:
> 
> config ARM_THUMB
>         bool "Support Thumb user binaries" if !THUMBONLY_CPU
>         depends on CPU_ARM720T || CPU_ARM740T || CPU_ARM920T || \
> 		   CPU_ARM922T || CPU_ARM925T || CPU_ARM926T || \
> 		   CPU_ARM940T || CPU_ARM946E || CPU_ARM1020 || \
> 		   CPU_ARM1020E || CPU_ARM1022 || CPU_ARM1026 || \
> 		   CPU_XSCALE || CPU_XSC3 || CPU_MOHAWK || CPU_V6 || \
> 		   CPU_V6K || CPU_V7 || CPU_FEROCEON || THUMBONLY_CPU
>         default y
> 
> And... I'm left wondering - should we have this instead:
> 
> config CPU_ARM
> 	bool
> 
> config CPU_THUMB
> 	bool
> 
> which indicates whether the CPU supports the ARM instruction set or the
> Thumb instruction set (or both) - that should then allow us to select
> those from the individual CPU_xxx options and eliminate that big long
> list of dependencies against ARM_THUMB.
I like your idea and I will come up with a patch.

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |