[RFC] Fix omap3 booting with thumb2 compiled kernel

[Tony Lindgren]

* Grazvydas Ignotas <notasas at gmail.com> [150528 04:45]:
> On Thu, May 28, 2015 at 1:55 AM, Tony Lindgren <tony at atomide.com> wrote:
> > 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
> 
> moaps -> omaps

Thanks, fixed now. I also added a link for why ENDPROC is needed to the
description. I'll apply the patch below into fixes today.

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 omaps 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.

The reason why ENDPROC makes a difference is it sets .type and then
the compiler knows what to do with the thumb bit as explained at:

https://wiki.ubuntu.com/ARM/Thumb2PortingHowto

Reported-by: Kevin Hilman <khilman at kernel.org>
Tested-by: Kevin Hilman <khilman at linaro.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: