[RFC 5/8] powerpc/slb: Add documentation to runtime patching of SLB encoding

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

From: "khandual@linux.vnet.ibm.com" <khandual@linux.vnet.ibm.com>

This patch adds some documentation to 'patch_slb_encoding' function
explaining about how it clears the existing immediate value in the
given instruction and inserts a new one there.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
---
 arch/powerpc/mm/slb.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
index dcba4c2..8083a9e 100644
--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -278,7 +278,13 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
 static inline void patch_slb_encoding(unsigned int *insn_addr,
 				      unsigned int immed)
 {
-	int insn = (*insn_addr & 0xffff0000) | immed;
+	/*
+	 * Currently this patches only "li" and "cmpldi"
+	 * instructions with an immediate value. Here it
+	 * just clears the existing immediate value from
+	 * the instruction and inserts a new one there.
+	 */
+	unsigned int insn = (*insn_addr & 0xffff0000) | immed;
 	patch_instruction(insn_addr, insn);
 }
 
-- 
2.1.0