powerpc/pseries: Add extended_cede_processor() helper function.

This patch provides an extended_cede_processor() helper function
which takes the cede latency hint as an argument. This hint is to be passed
on to the hypervisor to cede to the corresponding state on platforms
which support it.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/lppaca.h

@@ -100,7 +100,14 @@ struct lppaca {
 	// Used to pass parms from the OS to PLIC for SetAsrAndRfid
 	u64	saved_gpr3;		// Saved GPR3                   x20-x27
 	u64	saved_gpr4;		// Saved GPR4                   x28-x2F
-	u64	saved_gpr5;		// Saved GPR5                   x30-x37
+	union {
+		u64	saved_gpr5;	/* Saved GPR5               x30-x37 */
+		struct {
+			u8	cede_latency_hint;  /*			x30 */
+			u8	reserved[7];        /*		    x31-x36 */
+		} fields;
+	} gpr5_dword;
+
 
 	u8	dtl_enable_mask;	// Dispatch Trace Log mask	x38-x38
 	u8	donate_dedicated_cpu;	// Donate dedicated CPU cycles  x39-x39

arch/powerpc/platforms/pseries/plpar_wrappers.h

@@ -9,11 +9,33 @@ static inline long poll_pending(void)
 	return plpar_hcall_norets(H_POLL_PENDING);
 }
 
+static inline u8 get_cede_latency_hint(void)
+{
+	return get_lppaca()->gpr5_dword.fields.cede_latency_hint;
+}
+
+static inline void set_cede_latency_hint(u8 latency_hint)
+{
+	get_lppaca()->gpr5_dword.fields.cede_latency_hint = latency_hint;
+}
+
 static inline long cede_processor(void)
 {
 	return plpar_hcall_norets(H_CEDE);
 }
 
+static inline long extended_cede_processor(unsigned long latency_hint)
+{
+	long rc;
+	u8 old_latency_hint = get_cede_latency_hint();
+
+	set_cede_latency_hint(latency_hint);
+	rc = cede_processor();
+	set_cede_latency_hint(old_latency_hint);
+
+	return rc;
+}
+
 static inline long vpa_call(unsigned long flags, unsigned long cpu,
 		unsigned long vpa)
 {

arch/powerpc/xmon/xmon.c

@@ -1641,7 +1641,8 @@ static void super_regs(void)
 			       ptrLpPaca->saved_srr0, ptrLpPaca->saved_srr1);
 			printf("    Saved Gpr3=%.16lx  Saved Gpr4=%.16lx \n",
 			       ptrLpPaca->saved_gpr3, ptrLpPaca->saved_gpr4);
-			printf("    Saved Gpr5=%.16lx \n", ptrLpPaca->saved_gpr5);
+			printf("    Saved Gpr5=%.16lx \n",
+				ptrLpPaca->gpr5_dword.saved_gpr5);
 		}
 #endif