x86: baytrail: Fix unstable ACPI S3 resume

It was observed that when booting a Ubuntu 16.04 kernel, doing ACPI
S3 suspend/resume sometimes causes the Ubuntu kernel hang forever.
The issue is however not reproduced with a kernel built from i386/
x86_64 defconfig configuration.

The unstability is actually caused by unexpected interrupts being
generated during the S3 resume. For some unknown reason, FSP (gold4)
for BayTrail configures the GPIO DFX5 PAD to enable level interrupt
(bit 24 and 25). As this pin keeps generating interrupts during an
S3 resume, and there is no IRQ requester in the kernel to handle it,
the kernel seems to hang and does not continue resuming.

Clear the mysterious interrupt bits for this pin.

Reported-by: Stefan Roese <sr@denx.de>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Stefan Roese <sr@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/x86/cpu/baytrail/valleyview.c

@@ -10,6 +10,13 @@
 #include <asm/irq.h>
 #include <asm/mrccache.h>
 #include <asm/post.h>
+#include <asm/arch/iomap.h>
+
+/* GPIO SUS */
+#define GPIO_SUS_PAD_BASE	(IO_BASE_ADDRESS + IO_BASE_OFFSET_GPSSUS)
+#define GPIO_SUS_DFX5_CONF0	0x150
+#define BYT_TRIG_LVL		BIT(24)
+#define BYT_TRIG_POS		BIT(25)
 
 #ifndef CONFIG_EFI_APP
 int arch_cpu_init(void)
@@ -33,6 +40,21 @@ int arch_misc_init(void)
 	mrccache_save();
 #endif
 
+	/*
+	 * For some unknown reason, FSP (gold4) for BayTrail configures
+	 * the GPIO DFX5 PAD to enable level interrupt (bit 24 and 25).
+	 * This does not cause any issue when Linux kernel runs w/ or w/o
+	 * the pinctrl driver for BayTrail. However this causes unstable
+	 * S3 resume if the pinctrl driver is included in the kernel build.
+	 * As this pin keeps generating interrupts during an S3 resume,
+	 * and there is no IRQ requester in the kernel to handle it, the
+	 * kernel seems to hang and does not continue resuming.
+	 *
+	 * Clear the mysterious interrupt bits for this pin.
+	 */
+	clrbits_le32(GPIO_SUS_PAD_BASE + GPIO_SUS_DFX5_CONF0,
+		     BYT_TRIG_LVL | BYT_TRIG_POS);
+
 	return 0;
 }