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

[Siarhei Siamashka]

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?

I guess, the next step would be to fix sunxi to use Thumb2
everywhere :-)

Now your patch at least makes sense and looks good to me.

Acked-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>

-- 
Best regards,
Siarhei Siamashka