ARM: 8327/1: zImage: add support for ARMv7-M

This patch makes it possible to enter zImage in Thumb mode for ARMv7-M
(Cortex-M) CPUs that do not support ARM mode. The kernel entry is also
made in Thumb mode.

[ukl: fix spelling in commit log, return early in call_cache_fn]
Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Tested-by: Stefan Agner <stefan@agner.ch>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/head.S

@@ -10,8 +10,11 @@
  */
 #include <linux/linkage.h>
 #include <asm/assembler.h>
+#include <asm/v7m.h>
+
+ AR_CLASS(	.arch	armv7-a	)
+ M_CLASS(	.arch	armv7-m	)
 
-	.arch	armv7-a
 /*
  * Debugging stuff
  *
@@ -114,7 +117,12 @@
  * sort out different calling conventions
  */
 		.align
-		.arm				@ Always enter in ARM state
+		/*
+		 * Always enter in ARM state for CPUs that support the ARM ISA.
+		 * As of today (2014) that's exactly the members of the A and R
+		 * classes.
+		 */
+ AR_CLASS(	.arm	)
 start:
 		.type	start,#function
 		.rept	7
@@ -133,13 +141,14 @@ start:
  THUMB(		.thumb			)
 1:
  ARM_BE8(	setend	be		)	@ go BE8 if compiled for BE8
-		mrs	r9, cpsr
+ AR_CLASS(	mrs	r9, cpsr	)
 #ifdef CONFIG_ARM_VIRT_EXT
 		bl	__hyp_stub_install	@ get into SVC mode, reversibly
 #endif
 		mov	r7, r1			@ save architecture ID
 		mov	r8, r2			@ save atags pointer
 
+#ifndef CONFIG_CPU_V7M
 		/*
 		 * Booting from Angel - need to enter SVC mode and disable
 		 * FIQs/IRQs (numeric definitions from angel arm.h source).
@@ -155,6 +164,7 @@ not_angel:
 		safe_svcmode_maskall r0
 		msr	spsr_cxsf, r9		@ Save the CPU boot mode in
 						@ SPSR
+#endif
 		/*
 		 * Note that some cache flushing and other stuff may
 		 * be needed here - is there an Angel SWI call for this?
@@ -827,6 +837,16 @@ __common_mmu_cache_on:
 call_cache_fn:	adr	r12, proc_types
 #ifdef CONFIG_CPU_CP15
 		mrc	p15, 0, r9, c0, c0	@ get processor ID
+#elif defined(CONFIG_CPU_V7M)
+		/*
+		 * On v7-M the processor id is located in the V7M_SCB_CPUID
+		 * register, but as cache handling is IMPLEMENTATION DEFINED on
+		 * v7-M (if existant at all) we just return early here.
+		 * If V7M_SCB_CPUID were used the cpu ID functions (i.e.
+		 * __armv7_mmu_cache_{on,off,flush}) would be selected which
+		 * use cp15 registers that are not implemented on v7-M.
+		 */
+		bx	lr
 #else
 		ldr	r9, =CONFIG_PROCESSOR_ID
 #endif
@@ -1328,7 +1348,8 @@ __hyp_reentry_vectors:
 __enter_kernel:
 		mov	r0, #0			@ must be 0
  ARM(		mov	pc, r4		)	@ call kernel
- THUMB(		bx	r4	)		@ entry point is always ARM
+ M_CLASS(	add	r4, r4, #1	)	@ enter in Thumb mode for M class
+ THUMB(		bx	r4		)	@ entry point is always ARM for A/R classes
 
 reloc_code_end:
 

arch/arm/include/asm/unified.h

@@ -24,6 +24,14 @@
 	.syntax unified
 #endif
 
+#ifdef CONFIG_CPU_V7M
+#define AR_CLASS(x...)
+#define M_CLASS(x...)	x
+#else
+#define AR_CLASS(x...)	x
+#define M_CLASS(x...)
+#endif
+
 #ifdef CONFIG_THUMB2_KERNEL
 
 #if __GNUC__ < 4