Subject: [RFC] Fix omap3 booting with thumb2 compiled kernel

From: [email-masked] (Tony Lindgren)
Date: Thu, 28 May 2015 13:41:25 -0700

* Arnd Bergmann <[email-masked]> [150528 11:57]:
> On Thursday 28 May 2015 09:36:05 Tony Lindgren wrote:
> > * Dave Martin <[email-masked]> [150528 09:19]:
> > > On Thu, May 28, 2015 at 07:21:25AM -0700, Tony Lindgren wrote:
> > > > --- a/arch/arm/mach-omap2/sleep34xx.S
> > > > +++ b/arch/arm/mach-omap2/sleep34xx.S
> > > > @@ -203,23 +203,8 @@ save_context_wfi:
> > > >      */
> > > >     ldr     r1, kernel_flush
> > > >     blx     r1
> > > > -   /*
> > > > -    * The kernel doesn't interwork: v7_flush_dcache_all in particluar will
> > > > -    * always return in Thumb state when CONFIG_THUMB2_KERNEL is enabled.
> > > > -    * This sequence switches back to ARM.  Note that .align may insert a
> > > > -    * nop: bx pc needs to be word-aligned in order to work.
> > > > -    */
> > > > - THUMB(    .thumb          )
> > > > - THUMB(    .align          )
> > > > - THUMB(    bx      pc      )
> > > > - THUMB(    nop             )
> > > > -   .arm
> > > > -
> > > 
> > > ^ This looks unrelated to the issue?  This code is simply unnecessary
> > > after Russell introduced the "ret" macro in commit 6ebbf2ce43.  That
> > > made v7_flush_dcache_all do a proper interworking return.
> > > 
> > > It should probably be in a separate commit, or at least mentioned
> > > explicitly in the commit log.
> > 
> > Thanks, I've updated the description with the commit info above.
> > 
> > I'll keep the removal of the duplicate code in this patch, as it's
> > all related to the mode switching and we don't want to do it twice.
> 
> I would have thought that the change is actually necessary after
> 6ebbf2ce43, because it now returns in ARM mode, which will cause the
> "bx pc; nop" thumb instruction sequence be misinterpreted as an 
> ARM instruction.

Could be it's necessary.. But alone that change is not enough.

Regards,

Tony