powerpc: Rename slb0_limit() to safe_stack_limit() and add Book3E support

slb0_limit() wasn't a very descriptive name. This changes it along with
a comment explaining what it's used for, and provides a 64-bit BookE
implementation.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/mmu-book3e.h

@@ -245,6 +245,10 @@ extern struct mmu_psize_def mmu_psize_defs[MMU_PAGE_COUNT];
 extern int mmu_linear_psize;
 extern int mmu_vmemmap_psize;
 
+#ifdef CONFIG_PPC64
+extern unsigned long linear_map_top;
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_MMU_BOOK3E_H_ */

arch/powerpc/kernel/setup_64.c

@@ -434,17 +434,30 @@ void __init setup_system(void)
 	DBG(" <- setup_system()\n");
 }
 
-static u64 slb0_limit(void)
+/* This returns the limit below which memory accesses to the linear
+ * mapping are guarnateed not to cause a TLB or SLB miss. This is
+ * used to allocate interrupt or emergency stacks for which our
+ * exception entry path doesn't deal with being interrupted.
+ */
+static u64 safe_stack_limit(void)
 {
-	if (mmu_has_feature(MMU_FTR_1T_SEGMENT)) {
+#ifdef CONFIG_PPC_BOOK3E
+	/* Freescale BookE bolts the entire linear mapping */
+	if (mmu_has_feature(MMU_FTR_TYPE_FSL_E))
+		return linear_map_top;
+	/* Other BookE, we assume the first GB is bolted */
+	return 1ul << 30;
+#else
+	/* BookS, the first segment is bolted */
+	if (mmu_has_feature(MMU_FTR_1T_SEGMENT))
 		return 1UL << SID_SHIFT_1T;
-	}
 	return 1UL << SID_SHIFT;
+#endif
 }
 
 static void __init irqstack_early_init(void)
 {
-	u64 limit = slb0_limit();
+	u64 limit = safe_stack_limit();
 	unsigned int i;
 
 	/*
@@ -497,7 +510,7 @@ static void __init emergency_stack_init(void)
 	 * bringup, we need to get at them in real mode. This means they
 	 * must also be within the RMO region.
 	 */
-	limit = min(slb0_limit(), ppc64_rma_size);
+	limit = min(safe_stack_limit(), ppc64_rma_size);
 
 	for_each_possible_cpu(i) {
 		unsigned long sp;