[PATCH v3] powerpc: Add an inline function to update POWER8 HID0

["Gautham R. Shenoy" <ego@linux.vnet.ibm.com>]

Section 3.7 of Version 1.2 of the Power8 Processor User's Manual
prescribes that updates to HID0 be preceded by a SYNC instruction and
followed by an ISYNC instruction (Page 91).

Create an inline function name update_power8_hid0() which follows this
recipe and invoke it from the static split core path.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
[v1 --> v2: Moved defn of update_hid0 to reg.h from kvm_ppc.h]
[v2 --> v3: Renamed to update_power8_hid0 and used asm volatile]

 arch/powerpc/include/asm/reg.h           | 9 +++++++++
 arch/powerpc/platforms/powernv/subcore.c | 4 ++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index af56b5c..1245d99 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1281,6 +1281,15 @@ struct pt_regs;
 
 extern void ppc_save_regs(struct pt_regs *regs);
 
+static inline void update_power8_hid0(unsigned long hid0)
+{
+	/*
+	 *  The HID0 update on Power8 should at the very least be
+	 *  preceded by a a SYNC instruction followed by an ISYNC
+	 *  instruction
+	 */
+	asm volatile("sync; mtspr %0,%1; isync":: "i"(SPRN_HID0), "r"(hid0));
+}
 #endif /* __ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_REG_H */
diff --git a/arch/powerpc/platforms/powernv/subcore.c b/arch/powerpc/platforms/powernv/subcore.c
index f60f80a..503a73f 100644
--- a/arch/powerpc/platforms/powernv/subcore.c
+++ b/arch/powerpc/platforms/powernv/subcore.c
@@ -190,7 +190,7 @@ static void unsplit_core(void)
 
 	hid0 = mfspr(SPRN_HID0);
 	hid0 &= ~HID0_POWER8_DYNLPARDIS;
-	mtspr(SPRN_HID0, hid0);
+	update_power8_hid0(hid0);
 	update_hid_in_slw(hid0);
 
 	while (mfspr(SPRN_HID0) & mask)
@@ -227,7 +227,7 @@ static void split_core(int new_mode)
 	/* Write new mode */
 	hid0  = mfspr(SPRN_HID0);
 	hid0 |= HID0_POWER8_DYNLPARDIS | split_parms[i].value;
-	mtspr(SPRN_HID0, hid0);
+	update_power8_hid0(hid0);
 	update_hid_in_slw(hid0);
 
 	/* Wait for it to happen */
-- 
1.9.3