[ARM] ARMv6: add CPU_HAS_ASID configuration

Presently, we check for the minimum ARM architecture that we're
building for to determine whether we need ASID support.  This is
wrong - if we're going to support a range of CPUs which include
ARMv6 or higher, we need the ASID.

Convert the checks to use a new configuration symbol, and arrange
for ARMv6 and higher CPU entries to select it.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/asm-offsets.c

@@ -85,7 +85,7 @@ int main(void)
   DEFINE(S_OLD_R0,		offsetof(struct pt_regs, ARM_ORIG_r0));
   DEFINE(S_FRAME_SIZE,		sizeof(struct pt_regs));
   BLANK();
-#if __LINUX_ARM_ARCH__ >= 6
+#ifdef CONFIG_CPU_HAS_ASID
   DEFINE(MM_CONTEXT_ID,		offsetof(struct mm_struct, context.id));
   BLANK();
 #endif

arch/arm/mm/Kconfig

@@ -351,6 +351,7 @@ config CPU_V6
 	select CPU_CACHE_V6
 	select CPU_CACHE_VIPT
 	select CPU_CP15_MMU
+	select CPU_HAS_ASID
 	select CPU_COPY_V6 if MMU
 	select CPU_TLB_V6 if MMU
 
@@ -476,6 +477,12 @@ config CPU_TLB_V6
 
 endif
 
+config CPU_HAS_ASID
+	bool
+	help
+	  This indicates whether the CPU has the ASID register; used to
+	  tag TLB and possibly cache entries.
+
 config CPU_CP15
 	bool
 	help

include/asm-arm/mmu.h

@@ -4,13 +4,13 @@
 #ifdef CONFIG_MMU
 
 typedef struct {
-#if __LINUX_ARM_ARCH__ >= 6
+#ifdef CONFIG_CPU_HAS_ASID
 	unsigned int id;
 #endif
 	unsigned int kvm_seq;
 } mm_context_t;
 
-#if __LINUX_ARM_ARCH__ >= 6
+#ifdef CONFIG_CPU_HAS_ASID
 #define ASID(mm)	((mm)->context.id & 255)
 #else
 #define ASID(mm)	(0)

include/asm-arm/mmu_context.h

@@ -19,7 +19,7 @@
 
 void __check_kvm_seq(struct mm_struct *mm);
 
-#if __LINUX_ARM_ARCH__ >= 6
+#ifdef CONFIG_CPU_HAS_ASID
 
 /*
  * On ARMv6, we have the following structure in the Context ID: