[PATCH V2] acpi: reboot: fix racing after writing to ACPI RESET_REG

[Zhang Rui <rui.zhang@intel.com>]

According to the ACPI spec, "The system must reset immediately following
the write to the ACPI RESET_REG register.", but there are cases that the
system does not follow this and results in racing with the subsequetial
reboot mechanism, which brings unexpected behavior.

Fix this by adding a 15ms delay after writing to the ACPI RESET_REG.

Reported-by: Ghorai, Sukumar <sukumar.ghorai@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
 drivers/acpi/reboot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c
index ca707f5b521d..0e357cb5612f 100644
--- a/drivers/acpi/reboot.c
+++ b/drivers/acpi/reboot.c
@@ -3,6 +3,7 @@
 #include <linux/pci.h>
 #include <linux/acpi.h>
 #include <acpi/reboot.h>
+#include <linux/delay.h>
 
 #ifdef CONFIG_PCI
 static void acpi_pci_reboot(struct acpi_generic_address *rr, u8 reset_value)
@@ -66,4 +67,13 @@ void acpi_reboot(void)
 		acpi_reset();
 		break;
 	}
+
+	/*
+	 * Some platforms do not shutdown immediately after writing to the
+	 * ACPI reset register, and this results in racing with the
+	 * subsequetial reboot mechanism.
+	 * Delay for 15ms has been proved to be long enough for the system
+	 * to reboot, for these platforms.
+	 */
+	mdelay(15);
 }
-- 
2.17.1