ARM: imx: add cpuidle support for i.mx6sl

Add cpuidle support for i.MX6SL, currently only support
two cpuidle levels(ARM wfi and WAIT mode), and add software
workaround for WAIT mode errata as below:

ERR005311 CCM: After exit from WAIT mode, unwanted interrupt(s) taken
          during WAIT mode entry process could cause cache memory
          corruption.

Software workaround:
    To prevent this issue from occurring, software should ensure that
the ARM to IPG clock ratio is less than 12:5 (that is < 2.4x), before
entering WAIT mode.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/cpuidle-imx6sl.c

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2014 Freescale Semiconductor, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/cpuidle.h>
+#include <linux/module.h>
+#include <asm/cpuidle.h>
+#include <asm/proc-fns.h>
+
+#include "common.h"
+#include "cpuidle.h"
+
+static int imx6sl_enter_wait(struct cpuidle_device *dev,
+			    struct cpuidle_driver *drv, int index)
+{
+	imx6q_set_lpm(WAIT_UNCLOCKED);
+	/*
+	 * Software workaround for ERR005311, see function
+	 * description for details.
+	 */
+	imx6sl_set_wait_clk(true);
+	cpu_do_idle();
+	imx6sl_set_wait_clk(false);
+	imx6q_set_lpm(WAIT_CLOCKED);
+
+	return index;
+}
+
+static struct cpuidle_driver imx6sl_cpuidle_driver = {
+	.name = "imx6sl_cpuidle",
+	.owner = THIS_MODULE,
+	.states = {
+		/* WFI */
+		ARM_CPUIDLE_WFI_STATE,
+		/* WAIT */
+		{
+			.exit_latency = 50,
+			.target_residency = 75,
+			.flags = CPUIDLE_FLAG_TIME_VALID |
+				CPUIDLE_FLAG_TIMER_STOP,
+			.enter = imx6sl_enter_wait,
+			.name = "WAIT",
+			.desc = "Clock off",
+		},
+	},
+	.state_count = 2,
+	.safe_state_index = 0,
+};
+
+int __init imx6sl_cpuidle_init(void)
+{
+	return cpuidle_register(&imx6sl_cpuidle_driver, NULL);
+}