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Under /proc/acpi, there is a fan control interface, a user can set 0 or 3 to /proc/acpi/fan/*/state, 0 denotes D0 state, 3 denotes D3 state, but in current implementation, a user can set a fan to D1 state by any char excluding '1', '2' and '3'. For example: [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: off [root@localhost acpi]# echo "" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: on [root@localhost acpi]# echo "3" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: off [root@localhost acpi]# echo "xxxxx" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: on Obviously, such inputs as "" and "xxxxx" are invalid for fan state. This patch fixes this issue, it strictly limits fan state only to accept 0, 1, 2 and 3, any other inputs are invalid. Before applying this patch, the test result is: [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: off [root@localhost acpi]# echo "" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: on [root@localhost acpi]# echo "3" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: off [root@localhost acpi]# echo "xxxxx" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: on [root@localhost acpi]# echo "3" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: off [root@localhost acpi]# echo "3x" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: off [root@localhost acpi]# echo "-1x" > /proc/acpi/fan/C31B/state [root@localhost acpi]# cat /proc/acpi/fan/C31B/state status: on [root@localhost acpi]# After applying this patch, the test result is: [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: off [root@localhost ~]# echo "" > /proc/acpi/fan/C31B/state -bash: echo: write error: Invalid argument [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: off [root@localhost ~]# echo "3" > /proc/acpi/fan/C31B/state [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: off [root@localhost ~]# echo "xxxxx" > /proc/acpi/fan/C31B/state -bash: echo: write error: Invalid argument [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: off [root@localhost ~]# echo "-1x" > /proc/acpi/fan/C31B/state -bash: echo: write error: Invalid argument [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: off [root@localhost ~]# echo "0" > //proc/acpi/fan/C31B/state [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: on [root@localhost ~]# echo "4" > //proc/acpi/fan/C31B/state -bash: echo: write error: Invalid argument [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: on [root@localhost ~]# echo "3" > //proc/acpi/fan/C31B/state [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: off [root@localhost ~]# echo "0" > //proc/acpi/fan/C31B/state [root@localhost ~]# cat /proc/acpi/fan/C31B/state status: on [root@localhost ~]# echo "3x" > //proc/acpi/fan/C31B/state -bash: echo: write error: Invalid argument [root@localhost ~]# Signed-off-by: Yi Yang <yi.y.yang@intel.com> Signed-off-by: Andi Kleen <ak@linux.intel.com> Acked-by: Zhang Rui <rui.zhang@intel.com> Signed-off-by: Len Brown <len.brown@intel.com>