[RFC] Fix omap3 booting with thumb2 compiled kernel

[Tony Lindgren]

* Kevin Hilman <khilman at kernel.org> [150527 15:20]:
> [ fix email for Dave Martin, +Tyler ]
> 
> Tony Lindgren <tony at atomide.com> writes:
> 
> > The power management related assembly needs to interact with
> > ARM mode bootrom code, so we need to keep most of the related
> > assembly in ARM mode.
> >
> > Currently we are entering into and ARM mode assembly function
> > from thumb2 mode, so we need to make sure we switch to ARM
> > mode. And we need to do that again after the cache flush.
> >
> > ---
> >
> > Kevin told me about this earlier today.. 
> 
> 
> And for full boot log/panics, see the kernelci.org thumb2 kernel boots
> that fail: http://kernelci.org/boot/?THUMB2_KERNEL&fail
> 
> > Anybody got better ideas for a fix here?
> 
> FWIW, a quick test of this patch makes my omap3-beagle-xm pass a simple
> boot test, but it fails with off idle.

Thanks to Stephen Boyd's suggestion of checking the missing ENDPROC,
here's a better fix :) Now off idle works too.

Regards,

Tony

8 <----------------------
From: Tony Lindgren <tony at atomide.com>
Date: Wed, 27 May 2015 15:33:57 -0700
Subject: [PATCH] ARM: OMAP3: Fix booting with thumb2 kernel

We get a NULL pointer dereference on omap3 for thumb2 compiled kernels:

Internal error: Oops: 80000005 [#1] SMP THUMB2
...
[<c046497b>] (_raw_spin_unlock_irqrestore) from [<c0024375>]
(omap3_enter_idle_bm+0xc5/0x178)
[<c0024375>] (omap3_enter_idle_bm) from [<c0374e63>]
(cpuidle_enter_state+0x77/0x27c)
[<c0374e63>] (cpuidle_enter_state) from [<c00627f1>]
(cpu_startup_entry+0x155/0x23c)
[<c00627f1>] (cpu_startup_entry) from [<c06b9a47>]
(start_kernel+0x32f/0x338)
[<c06b9a47>] (start_kernel) from [<8000807f>] (0x8000807f)

The power management related assembly on moaps needs to interact with
ARM mode bootrom code, so we need to keep most of the related assembly
in ARM mode.

Turns out this error is because of missing ENDPROC for assembly code
as suggested by Stephen Boyd <sboyd at codeaurora.org>. Let's add the
missing ENDPROC in two places to sleep34xx.S, and also remove the
earlier mystery code that was probably also caused by missing ENDPROC
for earlier kernels.

Reported-by: Kevin Hilman <khilman at kernel.org>
Signed-off-by: Tony Lindgren <tony at atomide.com>

--- 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
-
 	b	omap3_do_wfi
-
-/*
- * Local variables
- */
+ENDPROC(omap34xx_cpu_suspend)
 omap3_do_wfi_sram_addr:
 	.word omap3_do_wfi_sram
 kernel_flush:
@@ -364,10 +349,7 @@ exit_nonoff_modes:
  * ===================================
  */
 	ldmfd	sp!, {r4 - r11, pc}	@ restore regs and return
-
-/*
- * Local variables
- */
+ENDPROC(omap3_do_wfi)
 sdrc_power:
 	.word	SDRC_POWER_V
 cm_idlest1_core: