ARM: imx: replace imx6q_restart() with mxc_restart()

The imx6q_restart() works fine with normal reboot but will run into
problem with emergency reboot like sysrq-b.  In that case, of_iomap()
gets called from interrupt context and hence triggers the BUG_ON in
__get_vm_area_node().

Actually, since commit c1e31d12 (ARM: imx: create
mxc_arch_reset_init_dt() for DT boot), imx6q/dl should try to use
mxc_restart() by calling mxc_arch_reset_init_dt() beforehand, where
things like of_iomap() can be done.

The patch updates mxc_restart() a little bit to get it work for imx6q/dl
and kill imx6q_restart() completely.
Reported-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/common.h

@@ -126,7 +126,11 @@ static inline void imx_smp_prepare(void) {}
 static inline void imx_scu_standby_enable(void) {}
 #endif
 extern void imx_src_init(void);
+#ifdef CONFIG_HAVE_IMX_SRC
 extern void imx_src_prepare_restart(void);
+#else
+static inline void imx_src_prepare_restart(void) {}
+#endif
 extern void imx_gpc_init(void);
 extern void imx_gpc_pre_suspend(void);
 extern void imx_gpc_post_resume(void);

arch/arm/mach-imx/mach-imx6q.c

@@ -13,7 +13,6 @@
 #include <linux/clk.h>
 #include <linux/clkdev.h>
 #include <linux/cpu.h>
-#include <linux/delay.h>
 #include <linux/export.h>
 #include <linux/init.h>
 #include <linux/io.h>
@@ -38,36 +37,6 @@
 #include "cpuidle.h"
 #include "hardware.h"
 
-static void imx6q_restart(enum reboot_mode mode, const char *cmd)
-{
-	struct device_node *np;
-	void __iomem *wdog_base;
-
-	np = of_find_compatible_node(NULL, NULL, "fsl,imx6q-wdt");
-	wdog_base = of_iomap(np, 0);
-	if (!wdog_base)
-		goto soft;
-
-	imx_src_prepare_restart();
-
-	/* enable wdog */
-	writew_relaxed(1 << 2, wdog_base);
-	/* write twice to ensure the request will not get ignored */
-	writew_relaxed(1 << 2, wdog_base);
-
-	/* wait for reset to assert ... */
-	mdelay(500);
-
-	pr_err("Watchdog reset failed to assert reset\n");
-
-	/* delay to allow the serial port to show the message */
-	mdelay(50);
-
-soft:
-	/* we'll take a jump through zero as a poor second */
-	soft_restart(0);
-}
-
 /* For imx6q sabrelite board: set KSZ9021RN RGMII pad skew */
 static int ksz9021rn_phy_fixup(struct phy_device *phydev)
 {
@@ -167,6 +136,8 @@ static void __init imx6q_init_machine(void)
 	imx_print_silicon_rev(cpu_is_imx6dl() ? "i.MX6DL" : "i.MX6Q",
 			      imx_get_soc_revision());
 
+	mxc_arch_reset_init_dt();
+
 	parent = imx_soc_device_init();
 	if (parent == NULL)
 		pr_warn("failed to initialize soc device\n");
@@ -285,5 +256,5 @@ DT_MACHINE_START(IMX6Q, "Freescale i.MX6 Quad/DualLite (Device Tree)")
 	.init_machine	= imx6q_init_machine,
 	.init_late      = imx6q_init_late,
 	.dt_compat	= imx6q_dt_compat,
-	.restart	= imx6q_restart,
+	.restart	= mxc_restart,
 MACHINE_END

arch/arm/mach-imx/system.c

@@ -42,6 +42,9 @@ void mxc_restart(enum reboot_mode mode, const char *cmd)
 {
 	unsigned int wcr_enable;
 
+	if (cpu_is_imx6q() || cpu_is_imx6dl())
+		imx_src_prepare_restart();
+
 	if (wdog_clk)
 		clk_enable(wdog_clk);
 
@@ -52,6 +55,8 @@ void mxc_restart(enum reboot_mode mode, const char *cmd)
 
 	/* Assert SRS signal */
 	__raw_writew(wcr_enable, wdog_base);
+	/* write twice to ensure the request will not get ignored */
+	__raw_writew(wcr_enable, wdog_base);
 
 	/* wait for reset to assert... */
 	mdelay(500);