powerpc: Document sysfs DSCR interface

Add some documentation about ...

/sys/devices/system/cpu/dscr_default
/sys/devices/system/cpu/cpuN/dscr

... to Documentation/ABI/stable.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/Documentation/ABI/stable/sysfs-devices-system-cpu b/Documentation/ABI/stable/sysfs-devices-system-cpu
new file mode 100644 (file)
index 0000000..33c133e
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-devices-system-cpu
@@ -0,0 +1,25 @@
+What:          /sys/devices/system/cpu/dscr_default
+Date:          13-May-2014
+KernelVersion: v3.15.0
+Contact:
+Description:   Writes are equivalent to writing to
+               /sys/devices/system/cpu/cpuN/dscr on all CPUs.
+               Reads return the last written value or 0.
+               This value is not a global default: it is a way to set
+               all per-CPU defaults at the same time.
+Values:                64 bit unsigned integer (bit field)
+
+What:          /sys/devices/system/cpu/cpu[0-9]+/dscr
+Date:          13-May-2014
+KernelVersion: v3.15.0
+Contact:
+Description:   Default value for the Data Stream Control Register (DSCR) on
+               a CPU.
+               This default value is used when the kernel is executing and
+               for any process that has not set the DSCR itself.
+               If a process ever sets the DSCR (via direct access to the
+               SPR) that value will be persisted for that process and used
+               on any CPU where it executes (overriding the value described
+               here).
+               If set by a process it will be inherited by child processes.
+Values:                64 bit unsigned integer (bit field)