linux-kernel - [PATCH] ARM: OMAP5: Switch to THUMB mode if needed on secondary CPU

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Date:	Tue, 22 Apr 2014 13:31:46 -0500
From:	Joel Fernandes <joelf@...com>
To:	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	Joel Fernandes <joelf@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Russell King <linux@....linux.org.uk>,
	Nishanth Menon <nm@...com>, Tony Lindgren <tony@...mide.com>
Subject: [PATCH] ARM: OMAP5: Switch to THUMB mode if needed on secondary CPU

On my DRA7 system, when the kernel is built in THUMB mode, the secondary CPU
(Cortex A15) fails to come up causing SMP boot on second CPU to timeout. This
seems to be because the CPU is in ARM mode once the ROM hands over control to
the kernel.  Switch to THUMB mode if required once the kernel is control of
secondary CPU. On OMAP4 on the other hand, it appears to be in THUMB mode on
entry so this is not required and SMP boot works as is.

Cc: Santosh Shilimkar <santosh.shilimkar@...com>
Cc: Russell King <linux@....linux.org.uk>
Cc: Nishanth Menon <nm@...com>
Cc: Tony Lindgren <tony@...mide.com>
Signed-off-by: Joel Fernandes <joelf@...com>
---
 arch/arm/mach-omap2/omap-headsmp.S |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mach-omap2/omap-headsmp.S b/arch/arm/mach-omap2/omap-headsmp.S
index 75e9295..1809dce 100644
--- a/arch/arm/mach-omap2/omap-headsmp.S
+++ b/arch/arm/mach-omap2/omap-headsmp.S
@@ -1,7 +1,7 @@
 /*
  * Secondary CPU startup routine source file.
  *
- * Copyright (C) 2009 Texas Instruments, Inc.
+ * Copyright (C) 2014 Texas Instruments, Inc.
  *
  * Author:
  *      Santosh Shilimkar <santosh.shilimkar@...com>
@@ -28,9 +28,13 @@
  * code.  This routine also provides a holding flag into which
  * secondary core is held until we're ready for it to initialise.
  * The primary core will update this flag using a hardware
-+ * register AuxCoreBoot0.
+ * register AuxCoreBoot0.
  */
 ENTRY(omap5_secondary_startup)
+.arm
+THUMB( adr     r9, BSYM(wait)  )       @ CPU may be entered in ARM mode.
+THUMB( bx      r9              )       @ If this is a Thumb-2 kernel,
+THUMB( .thumb                  )       @ switch to Thumb now.
 wait:	ldr	r2, =AUX_CORE_BOOT0_PA	@ read from AuxCoreBoot0
 	ldr	r0, [r2]
 	mov	r0, r0, lsr #5
-- 
1.7.9.5

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