[PATCH 4/5] powerpc, dscr: Added some in-code documentation

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

This patch adds some in-code documentation to the DSCR related
code to make it more readable without having any functional
change to it.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/processor.h |  8 ++++++++
 arch/powerpc/kernel/sysfs.c          | 13 +++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index dda7ac4..81c1aeb 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -295,6 +295,14 @@ struct thread_struct {
 #endif
 #ifdef CONFIG_PPC64
 	unsigned long	dscr;
+	/*
+	 * XXX: dscr_inherit indicates that the process has explicitly
+	 * attempted and changed the DSCR register value for itself.
+	 * Hence kernel wont use the default CPU DSCR value contained
+	 * in the PACA structure anymore during process context switch.
+	 * Once this variable is set, this behaviour will be inherited
+	 * to all the children of this process from that point onwards.
+	 */
 	int		dscr_inherit;
 	unsigned long	ppr;	/* used to save/restore SMT priority */
 #endif
diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 67fd2fd..edde3f0 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -496,8 +496,21 @@ static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
 static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
 static DEVICE_ATTR(pir, 0400, show_pir, NULL);
 
+/*
+ * XXX: This is the system wide DSCR register default value.
+ * Any change to this value through the sysfs interface will
+ * update all per-cpu DSCR default values across the system
+ * stored in their respective PACA structures.
+ */
 static unsigned long dscr_default;
 
+/*
+ * XXX: read_dscr and write_dscr are the functions for the
+ * per-cpu DSCR default sysfs files present for each cpu.
+ * Though updates to per-cpu DSCR value also gets called
+ * for all the CPUs on the system when the system wide
+ * global dscr_default gets changed.
+ */
 static void read_dscr(void *val)
 {
 	*(unsigned long *)val = get_paca()->dscr_default;
-- 
1.9.3