[U-Boot] [PATCH 1/1] arm: Migrate SYS_THUMB_BUILD to Kconfig, introduce SPL_SYS_THUMB_BUILD

[Tom Rini]

On Tue, Mar 07, 2017 at 03:02:05AM +0200, Siarhei Siamashka wrote:
> On Mon, 6 Mar 2017 17:54:17 -0500
> Tom Rini <trini at konsulko.com> wrote:
> 
> > On Tue, Mar 07, 2017 at 12:44:59AM +0200, Siarhei Siamashka wrote:
> > > Hi Tom,
> > > 
> > > On Mon,  6 Mar 2017 13:50:10 -0500
> > > Tom Rini <trini at konsulko.com> wrote:
> > >   
> > > > Today, we have cases where we wish to build all of U-Boot in Thumb2 mode for
> > > > various reasons.  We also have cases where we only build SPL in Thumb2 mode due
> > > > to size constraints and wish to build the rest of the system in ARM mode.  
> > > 
> > > Is there a good real world example of this particular use case? Even if
> > > there is enough space for having the U-Boot binary built in ARM mode,
> > > Thumb2 is still smaller and loads faster. And having reduced boot time
> > > is always nice.  
> > 
> > So, good question.  At the moment, I'm not trying to change existing
> > behavior.  I also seem to recall that Thumb2 being a performance win
> > depends on what you're doing.  It would certainly be worth doing some
> > tests to see if on say Allwinner where today we don't do the main U-Boot
> > in Thumb2 mode there is a noticable change as it looked like a pretty
> > big size win.
> 
> Hmm, you are right. Currently the 'sunxi-common.h' file has the
> following lines:
> 
>   #if defined(CONFIG_SPL_BUILD) && !defined(CONFIG_ARM64)
>   #define CONFIG_SYS_THUMB_BUILD  /* Thumbs mode to save space in SPL */
>   #endif
> 
> I even did not know and was not careful enough to ever notice that sunxi
> builds the main U-Boot binary in ARM mode. This just seems to be weird.
> Basically, you are introducing two separate Kconfig options just to
> accommodate the current sunxi configuration, right?

Along with some at91 (arm926ej-s based) platforms.  In all cases the
root problem was "Oh, we can't fit SPL in our size constraint, lets
tweak it like this".

-- 
Tom
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