ARM: pm: preallocate a page table for suspend/resume

Preallocate a page table and setup an identity mapping for the MMU
enable code.  This means we don't have to "borrow" a page table to
do this, avoiding complexities with L2 cache coherency.

Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/suspend.c

@@ -0,0 +1,48 @@
+#include <linux/init.h>
+
+#include <asm/pgalloc.h>
+#include <asm/pgtable.h>
+#include <asm/memory.h>
+#include <asm/suspend.h>
+#include <asm/tlbflush.h>
+
+static pgd_t *suspend_pgd;
+
+extern int __cpu_suspend(int, long, unsigned long, int (*)(unsigned long));
+extern void cpu_resume_turn_mmu_on(void);
+
+/*
+ * Hide the first two arguments to __cpu_suspend - these are an implementation
+ * detail which platform code shouldn't have to know about.
+ */
+int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
+{
+	struct mm_struct *mm = current->active_mm;
+	int ret;
+
+	if (!suspend_pgd)
+		return -EINVAL;
+
+	/*
+	 * Temporarily switch the page tables to our suspend page
+	 * tables, which contain the temporary identity mapping
+	 * required for resuming.
+	 */
+	cpu_switch_mm(suspend_pgd, mm);
+	ret = __cpu_suspend(0, PHYS_OFFSET - PAGE_OFFSET, arg, fn);
+	cpu_switch_mm(mm->pgd, mm);
+	local_flush_tlb_all();
+
+	return ret;
+}
+
+static int __init cpu_suspend_init(void)
+{
+	suspend_pgd = pgd_alloc(&init_mm);
+	if (suspend_pgd) {
+		unsigned long addr = virt_to_phys(cpu_resume_turn_mmu_on);
+		identity_mapping_add(suspend_pgd, addr, addr + SECTION_SIZE);
+	}
+	return suspend_pgd ? 0 : -ENOMEM;
+}
+core_initcall(cpu_suspend_init);